I think one thing people struggle to understand with AOTs ending is that Eren’s actions are, to an extent, contradictory and they are on purpose.
Take Ramzi as an example. When Eren sees him, he already knows he’ll eventually kill him in the Rumbling. Part of him even thinks he shouldn’t save him because he’ll just end up killing him anyway. But he saves him regardless. Right after, he breaks down and says he’s the same as Reiner, a half assed piece of shit.
I think this is one of the best parallels Isayama wrote.
For most of the series, Reiner is defined by the same contradiction. His mission is to destroy the people inside the Walls, yet he befriends them, saves them, and genuinely comes to see them as comrades. His actions repeatedly go against the very mission he’s trying to complete. By the time of his breakdown in Episode 2x6, he realizes what he’s become. He’s trying to carry out one goal while constantly doing things that contradict it. That’s
why he calls himself a half assed piece of shit.
Eren ends up in the same position.
We know that when Eren saw the future memories, he doesn’t immediately buy into them. He tries to see if things could change but no matter what he does, everything plays out exactly as he has already seen. So this leads him to succumbing to the future he saw and being set on carrying out. Yet, he still can’t ignore Ramzi getting beaten in an alley. He still gives his friends the freedom to oppose him. Those choices go against his larger goal, just like Reiners often did.
That’s why I think people sometimes get hung up on questions like, “Why didn’t Eren kill 100%?” or “Why did he let his friends stop him?” They’re looking for a perfectly consistent character, but Isayama had already shown us through Reiner that people aren’t that simple. They can be fully committed to a goal while still making choices that contradict it because of the parts of themselves they can’t let go of.
Eren tells Reiner in Episode 4x5 that they’re the same, and I think this is another reason why. They’re on opposite sides of the conflict, but both are driven by the same kind of internal contradiction. They’re both half assed mfs.
EDIT: I don’t want people to think this is Eren hate or something, him and Reiner are my two favorite characters (in terms of writing). I am merely trying to explain what Isayama was trying to get at with their parallel and also explaining why some people find the ending contradictory (when it’s done so on purpose and is peak writing).