1) Finn was useless at a Storm Trooper standpoint.
2) His escaped is not a keypoint, it's just a plot device to save Poe.
3) Got ass kicked by everyone ( Rey, BB-8, the big pig when he was drinking, Chewie, the beast in Solo space ship, Kylo Ren etc... )
4) He's a bad fighter.
5 ) He's using humour to hide his weakness.
6 ) Everything could have been done without him beside saving Poe/evacuating from Jakku even if Rey could probably have save herself.
7) He was saved by Rey X times...
8) He almost died at the end.
I know some people will disagree but I won't change my mind on him much, I like the character and I think he has the potential to be everything in the series but for now, he's useless and not really what I was waiting for at character standpoint.
My thoughts on your points:
1) We only see Finn as a Stormtrooper for a brief moment at the beginning, but he was far from terrible at it. We see him man turrets, use a blaster to kill some fellow Stormtroopers (during the Maz temple attack), and hold his own against a melee trooper, and Kylo Ren. That wasn't Finn training, that was a result of his Stormtrooper background. Phasma said he never had any problems before, and yes, he was in sanitation on Starkiller base, but any military man will tell you that they've held a lot of different jobs during their time. Also, he was a solider is Phasma's squad of Stormtroopers sent to ransack the Jakku village to recover insanely important data. They would not have just handed that job off to any crew. It was Phasma's crew, implying Finn not being your run of the mill, joe average trooper.
2) Not true in the slightest. Him escaping and turning informs his very character. It was massively important to his development as a hero. He broke his conditioning and freed himself from the First Order. Poe was more of a plot device, in that he is holding key information to finding Luke, and Finn needed a pilot to help him escape. Poe also demonstrates that plot devices can be incredibly likable characters...
3) Rey surprised him and knocked him on his ass while he wasn't looking. That's not getting his ass handed to him, that's getting the drop dropped on you. BB-8 and Finn had no interaction in the movie in which he was bested by him. That's you grasping for another straw in the "Finn is holding those L's" narrative that is obnoxiously prevalent in discussion boards. The Rathar was a comedic beat, and played out as such, just like with BB-8. While sure, the Rathar's are dangerous, the scene is hardly framed as anything more serious than typical Star Wars shenanigans. Hell, Luke got grabbed by a tentacle monster in A New Hope, and only "won," because the monster let him go, not because he bested it in battle. That moment in ANH was played more for tension than the Rathar sequence.
He
did get knocked on his ass by the Riot trooper, but we don't know how that fight would have ended, because the trooper got killed by Han, and shortly after that, they
all got surrounded by troopers, and their weapons taken away. After that, Poe shows up, and during the fight, Finn kills some Stormtrooper with a blaster, a weapon he seems more comfortable with than a lightsaber, despite his melee training. He got beat by Kylo because Kylo knows how to use a lightsaber better than him. The point of that fight wasn't to have Finn "win," it was a defining moment for his character, because it showed that, despite going up against a more experienced fighter, he was willing to die to help his new friend. Finn didn't fight Kylo expecting to win, but he was trying to defend Rey, thus finding something to fight for after all. It was the moment he stopped "running" as Maz told him. He faced his past head on. Narratively, there was no way Finn was winning that fight, and not because it wasn't his story, but because it was a situation in which someone wasn't going to walk out of there alive. Either Kylo or Rey/Finn. It's the first movie in a trilogy. Rey didn't really win that fight either. She got a burst of adrenaline and force awareness, but before the battle could finish, the earth opened up and they were separated. It's very possible Kylo would have rallied, and taken advantage of her hesitation to kill him. That fight isn't over yet.
4) Far from it. A bad fighter would have had the shit knocked out of him moments from engaging the superior fighter. Finn held his own against the riot trooper until the trooper got a lucky hit on him with his stun baton (try coming back from a fight after a few thousand volts of electricity have coursed through your body), and he held his own against Kylo Ren for way longer than even Kylo was expecting. Even so, this point is more like an extension of your above post, not a separate point, and was used to pad your list.
5) Not even. Finn saved Poe. Finn was the gunner while Rey piloted the Falcon. If he hadn't been taking out the Tie Fighters, there's no doubt that one or more of them would have gotten a lucky hit on the Falcon and disabled it, or caused it to crash, killing Rey. It was also Finn that convinced the others to send him to Starkiller to disable the shields, when he really just wanted to rescue Rey. Yes, Rey rescued herself, but unless she lucked out with a ship, there was a big chance she'd have encountered Kylo again, he may have bested her, taking her to Snoke, or killed her, the Starkiller base wouldn't have been destroyed (it was his plan to capture Phasma and force her to lower the shield generators; another Resistance soldier may not have known to try that tactic). Finn was important to the narrative in more ways than just how many heroic moments he had. His relationships with Poe/Rey/Han are important to not only the development of those characters, but his own as well. He goes from a man fleeing his past, to facing it and persevering, even if he does end up TKO'd at the end. He's one of the most heroic and relatable characters in the film.
6) Who cares? A lot of people were saved by a lot of people throughout the movie. Poe was saved by Finn. Finn was saved by Rey. Han/Finn/Chewie were saved by Poe. Finn was saved by Han. Rey was saved by The Force/her own resourcefulness. In every ensemble cast action movie, characters will be captured, rescued, saved, etc by others or saving themselves. It's just...not as important. What does it matter if it was Rey that saved him. The fact that Finn didn't save Rey, but attempted to was another moment that established the bond between Finn and Rey. She was genuinely moved that he came back for her. It was a moment of growth for Finn that he'd risk his life for her. Succeeding or failing in saving her wasn't the point of the action. The point was the building of the relationship of Finn and Rey. How that occurs is up to the screenwriter. The result was going to be the same whether Finn saved her or not: Finn/Rey grow closer. This is how it would have played out:
A) Finn saves Rey: "Thank you for saving me, Finn! You're a good friend! We are now closer!"
B) Rey saves herself, and bumps into Finn (which happened in the movie): "Thank you for coming back for me, Finn! I didn't know that I meant that much to you! You willingly put yourself in harms way for me! I'm grateful! We are now closer!"
The latter is a lot more dramatic, and opens the door for characterization of both Rey
and Finn. Basically, it was a much more effective use of the situation because it served to enhance both characters, not just one. Finn also gave the Resistance vital information on Starkiller base that they would not have gotten when they got it had he not been present to give it to them.
8) Luke almost died at the end of The Empire Strikes Back? And? Once again, the point isn't that Finn wins every encounter he's in, but how those encounters inform and shape his character going forward. We don't know how his loss to Kylo is going to affect him, because episode 8 isn't out for another year and a half. More than likely, he is going to try and keep a situation like that from happening again. How that happens is yet to be seen. If he is Force Sensitive, then he'll probably seek out ways to train in the Force (probably through Maz, while Rey is with Luke). If not Force Sensitive, then he'll train in other ways, maybe learning to be a better melee fighter, a better pilot, a better marksman, who knows. His character arc is wide open looking at where we left him in TFA. He's no longer a Stormtrooper, but he has learned to fight for those he cares about, even loves. Winning or losing the fight against Kylo wouldn't have changed that character arc trajectory. Here's another set of scenarios:
A) Finn somehow managed to beat Kylo: "Woot! I beat you! I have overcome one of the biggest obstacles I will ever face, being a lowly sanitation worker/Stormtrooper! In episode 8, I will continue to rack up wins, and probably smooch Rey a lot, since I've learned the value of friendship, and have someone to fight for and protect!"
B) Finn loses to Kylo: "I was knocked on my ass by a much more skilled and dangerous foe. I need to not get owned again, so I'm going to try and better myself so the next time we meet, Kylo won't steamroll over me.
The former scenario is boring as fuck. Having a hero who constantly wins becomes boring and predictable. Look at Batman, James Bond, Superman, etc. While those characters are iconic and cool, the fact that they always come out on top makes their adventures less exciting for a lot of people (me included). We want to see our heroes fall, get up, fall, and get up again. The latter, and current scenario for Finn sets up a much more interesting arc and dynamic for both he and Kylo. Kylo bested him, so a second match could easily have Kylo underestimating the now determined and battle hardened Finn. It can add tension to the fight. I see the same for Kylo/Rey. Rey got the upper hand on Kylo, which could lead her into believing she can best him again. I imagine their second encounter is going to be far more in the favor of Kylo than Rey.
The second act is always where shit hits the fan for our hero/heroine. I think Rey is going to suffer a patented Skywalker limb loss in 8, and maybe Finn will actually successfully fend off Kylo while Rey is incapacitated (and no, that doesn't suddenly make Rey a damsel in need of saving, it helps round out her character by having her suffer a crushing loss after such a heroic victory, and sets up the stage for her to come back even better and more determined in 9. There's also some nice poetic symmetry to having Finn actually get the upper hand on Kylo this time, a mirror to their previous encounter. Star Wars loves its parallels). Hell, he could still lose and die at the end, but we have no idea, and a heroic death could still have some narrative power (I'm not expecting him to die in 8 or 9, realistically).
Creating a story with well rounded and 3 dimensional characters requires the writer to consider how the actions of the characters affect not only their character arcs, but the arcs of the characters that intersect one another throughout the story. TFA is actually well designed in that aspect, as the various character arcs are both influenced by, and independent of, one another. Kylo's arc was going a certain way, until he encountered Rey. Rey's arc was going a certain way until she encountered Finn. Fin's arc was going a certain way until he encountered Rey. Poe's arc was going a certain way until he encountered Finn. Rey/Poe/Finn's arcs were all going a certain way until they encountered Kylo Ren, etc, etc. Now that the characters and arcs are set up, the fun stuff gets to happen in Episode 8. That's going to be the real meat of this new trilogy, and it could go any way for any character:
Kylo is going into training with Snoke, who he disappointed at least three times throughout the movie. He is going to further sink into the well of the dark side and it's powers, making him more dangerous.
Rey is going into training with Luke, who she clearly has some kind of connection to that will influence the flow of her training (how will Rey handle whatever truths Luke has to tell her concerning his exile, her abandonment on Jakku, etc?). While Kylo is getting stronger, is she? Or is her training not going as well as her or Luke hope/need it to go?
Finn is going to recover from his wounds, and seek out betterment, maybe his lost family, maybe he and Poe go on a Resistance mission, who knows. Is he Force Sensitive? And if he is, does he even want to be a Jedi? Having force powers don't automatically mean you must become a Jedi. Luke became a Jedi because his father was, and he wanted to be like his "war hero" dad. Rey may not even want to become a Jedi herself. What if she decides she doesn't want to become a Jedi, but Finn decides he does want to become a Jedi? Being a Jedi isn't always the end game of a force user. Maz clearly has force abilities, but she is no Jedi. Rey may decide the monk's life isn't for her. Finn may decide it is. The point is that the door is open for all of them to have interesting, compelling arcs.
None of this would have been possible had TFA not nailed the characterization of Finn/Rey/Kylo. Much like Luke in A New Hope, the potential of our leads won't be seen/felt until the middle movie. Finn is hardly a useless character. He's arguably the best character in a film full of great characters. That's fricking impressive.