i dont think u can argue that aot cynically and dejectedly posits human nature as inherently selfish and self serving when the final arc is literally the protagonists risking everything and sacrificing all of the benefits they wouldve gained from eren’s actions to stop it. the story frames it so they r the unambiguous beneficiaries of a massive massacre (this was at the root of the changed infamous “thank u hitler” armin panel too sghsjshh) and in a position that makes stopping it extremely difficult and risky and requiring multiple very personal sacrifices on their part. on top of the dangerous position that stopping it after it had already started puts them in, all of them r made to be under the impression of having legitimately 0 personal stakes/benefits in stopping it. on the plane the warriors r deliberately made to believe that their families were already crushed with the fall of marley and liberio, with only the rest of the world, a world that showed them only hate, hostility, and suffering, at stake. they make the choice to continue trying to do what they do in that context. even annie, the character who consistently spouted and held this exact cynical understanding of human nature, makes the decision at the end to go back despite being under the impression that she wont ever see her father again. them being rewarded by the narrative afterwards does not change that.
it is what differentiates them from, makes them contradict, and sets them in opposition to eren and his fatalistic worldview and hatred of humanity and the self and selfishness anyway. everything that eren represents and embodies is written to be defeated by everything the alliance represents and embodies. the ending is about the possibility of that always being the case
