@LazloFF I wasn't considering them, I was considering the only currently known character with seemingly perfect future knowledge - that no matter what he did, he could not avoid what he saw. If that's the case, really he has probably already submitted to the pre-determined future, at least it seems so since he apparently tried to change a few things here and there in those flashbacks yet looked disappointed when he failed (though I'm only going off of other commenter's observations). In any case, there isn't a 'conclusion that Eren came to' in so much as it is the ONLY possible outcome assuming all things pre-determined.
And this is why it is convenient. It's a strange perspective that naturally exists if ANY character has absolute knowledge of the future. It's almost like spoilers, though not really. In my opinion, it feels a bit cheap, like this whole thing may as well have been a flashback, though it is certainly disguised very well.
Also why I had to, for a bit more of my own enjoyment, assume that Eren doesn't have that absolute knowledge. If it's only a small blip of time, then you've basically got "That's So Raven" happening lol. But depending on how far Eren has seen into this war, he may already know the genocide never took place/already succeeded etc.
To sum up, I only addressed the themes very briefly, but was more focused on the mechanical aspect of the storytelling itself. You seem to be properly immersed, however, so we're not really talking about the same thing.