They screwed themselves over when they tried to finish it in 13 episodes. Really, going back, a lot of glaring flaws started to pop up many seasons earlier. Just small things that didn't make a whole lot of sense. But when you don't have great writers, finishing something in a brief period of time is impossible. But the most unforgivable parts were wasting Jon's story and not even getting to fight the Night King. Even if he didn't kill him, them not even fighting after teasing it for like the entire series was a joke. A prisoner getting to pick the next king(like wtf). Grey Worm being the final boss. Like anyone would give a shit about Grey Worm. How Dany even had any men left to begin with after The Long Night. Just like characters started magically teleporting to save time, Dany kept magically having soldiers respawn. Ruined the character development of almost everyone.
But what I noted is precisely why a series like this isn't going to work. Jon's character being interesting was inexorably tied to the Night King. Everything he did in the show led toward the great battle and taking down the dead. Once they ruined that part by not even allowing him to fight and the Night King being gone, there is nothing left for Jon that's interesting. He's up in "the real north" with the wildlings with one eared Ghost. Ok, no one gives a shit. I guess they could have him head back south, as that whole part of the ending never made sense anyway. Grey Worm banished him to the north, and then sailed off into the sunset, so Jon could just be like ummm ok, so they're gone now, I really don't have to stay in the north anymore.