The first one, yes, it seems so. The second one, not quite - Sovereign claims that the Reapers built the Citadel and Mass Relays, while the Crucible has apparently been worked on by multiple civilizations across time. If there is some "proto-civilization," we are never told about it, which leads to the third point. We don't know of any such "dudes" - only the Catalyst claims that peace is impossible. The trouble is, assuming the first point still holds, why should we trust the Catalyst? What prevents him from being the voice of the Reaper, trying to indoctrinate a weak Shepard using the image of a child she has thought about all game long?
You're grapsing at straws, really. It's also impossible to survive being spaced and yet they revived Shepard in ME2. Even if his body should be disintegrated by entering the atmosphere of the planet his body crashed on. It's not like the series was always logical with such things. So Mass Effect 3 and ME2 are a huge hallucination while Shepard is being spaced out in ME2?
If they wanted a dream ending they would have explicitly made it so and there would still be a backlash because nothing is resolved. That means that you never confronted the illusive man, you never learn what the reapers want and are and you spent 75 hours of your life to make decisions that had no impact on the ending. They wouldn't also have added the sequence with the kid and grandpa in the end talking about the starts and other worlds if it was a dream.
Moreover, your dream sequence implies the catalyst lies and he doesn't. If you blow up the reapers, EDI will never show up during the ending sequence with the Normandy. She's toasted. I tried all three endings and for both the synthesis and control ending I get Joker, EDI and Kaidan in the end but in the destruction one I get Joker, Kaidan and Garrus.
There's no magic dream sequence. The Illusive Man is in the citadel in the end because he is indoctrinated by the reapers and they let him pass to get rid of Shepard in the eventuality he reached that spot. Since he's now a half reaper, he can indoctrinate/control both you and Anderson. You can break of his will either by forcing him to suicide by shooting him.
It might be grasping a little bit, I admit, but that might be just because the writers thought themselves too clever and didn't make this explicit enough. It's just as easy to believe that they crafted this clever ending and then neglected to make it clear, as it is to believe they made a shitty ending and thought people would be okay with it.
In this interpretation (remember, I've never called it anything more than that), your decisions
do impact the ending. If you built your EMS high enough, Shepard can survive the Destroy ending - only if you're strong enough, and only in that ending. Why would that be? Because your forces were strong enough to win, allowing Shepard to wake up rather than be annihilated. It's not perfect, but it's something.
Also, this interpretation assumes that the Catalyst is not a real thing, but a manifestation of Shepard's memories being exploited by the Reapers for indoctrination. If follows, then, that whatever happens after you choose is also not real, but Shepard imagining the impact of her decision. The Catalyst can still lie about EDI and the geth being destroyed, but Shepard
imagines that the Catalyst is correct; she takes his words at face value, when there is no reason to do so outside of being indoctrinated. Notice how in the "best" Destroy ending, you see people (and not EDI) walking out of the ship, but in the "bad" Destroy ending, no one leaves the ship. This could be a symbolic gesture: if you were strong enough, and Harbinger knows it, he tries to convince Shepard that he was right about synthetics being destroyed as a ditch effort at mockery; but if you're not strong enough, no one leaves the ship because actually, the assault failed on Earth and likely everyone died.
As far as TIM, why do we have to assume he is
actually there? Because he appears to be in front of us? He is indoctrinated, but what is to say that he actually made it, or that the Reapers didn't already dispose of him, and that his appearance is part of the manipulation? And if the Catalyst is misleading Shepard about Harbinger's control, why can't the Illusive Man's "exerted influence" (in the form of the shadowy substance on the screen) simply be Harbinger deflecting his influence on to another person, a person that Shepard
wants to see?
I admit that it's difficult to reconcile that sequence with the kid and grandpa. It's possible to say that it's part of Shepard imagining her influence in the far, far future. That's about all I can say about it right now; personally, I still think the scene detracts more than it adds.
However, I'm still surprised people accept the Cataylst's words without question. Why should we? Everything he says is a deflection of Shepard's goal. He takes a form that Shepard wants to see, a form that is easily manipulated. Shepard is literally lying a few yards away from Reaper tech - the same Reaper tech that we know can infiltrate people's minds and manipulate their thoughts. It's a completely thematically relevant idea that uses a common narrative trope - that of the red herring and unreliable narrator.