In that case, Eren's genocide solved the main conflict of the series.
Not by itself, no. It ended the Titans (... well, for quite some time, at the very least?), but that's it.
Armin and the others are the ones who resolved the main conflict of the series (or at the very least, I believe that's what the series implies, as I explained above).
I don't think (and I don't believe we're meant to think) that Eren's plan was the only one, and certainly not the best one either. I think it's pretty clear Armin was hoping for a peaceful resolution to the conflict, and as difficult as that would have been to achieve, I personally don't believe it was necessarily impossible. But Eren went ahead and utterly fucked
that up, so Armin and the others now have no choice but to make do with the hand they've been dealt.
My issue is that the story justified genocide by presenting it as a solution, or at the very least part of a solution, to the problems presented within the story. You seem to agree that this is the case, so that's something lol.
I think there should have been a clearer condemnation of Eren's genocide at the very end.
Yes, we've seen Armin comment about how Eren's attack on Liberio basically shattered any chance of a peaceful resolution of the conflict, and yes, Hans flat-out said that genocide was wrong,
period. But that was all before Eren revealed his exact plan/intentions.
I appreciate what Isayama did by turning everything on its head and going from "why are the Titans trying to destroy us, what could possibly be their intentions?" in the first two thirds of the story to the main mystery of the last third now being "what the fuck is
Eren thinking / trying to do?" I think it's a clever reversal. But it also means the reveal of Eren's intentions came very,
very late in the game, and as a result, I can see why readers would wonder "wait, we know what those characters said
earlier, but now that they know what Eren was trying to do, do they
still think it was wrong, or do they now think he was justified?"
I don't think Armin calling Eren's actions awful in that scene was enough (not even after Isayama changed the wording... that was a step in the right direction, sure,
but).
I think the fact he says that right after
thanking Eren is a problem. I appreciate what Isayama was trying to do, I agree that, considering their history, it wouldn't make sense for Armin to 100% condemn Eren in those circumstances, but I can absolutely see how confusing that may seem, why people would be too busy going "... wait, did he just
thank him?
what the fuck?" to even internalize the very next sentence. If that wasn't the right time for that,
just find another time, Isayama. Like, say, that scene on the boat, years later, for example. Have Armin say some of things I said above. Make it clear genocide wasn't awful just because it left a bad taste in Armin's mouth, but also because he still thinks there
would have been other, better ways. Make it clear that just because
Eren thought genocide was the only way, that doesn't mean it actually was.
And I don't like how Reiner and the others all seem to have the same kind of reaction to Eren's parting words. Armin is one thing: Eren and him were basically family. But characters like Reiner and Annie? If exploring their reactions to Eren's true intentions was not practical in terms of pacing (and I can see how it wouldn't be)... well, maybe just don't go there at all? Have Eren explain himself to Mikasa and Armin, and that's it. Don't imply he also talked to the rest of the cast. Seems a bit cold of him to just "ignore" the others? Yeah, well,
he just murdered 80% of the world's population. All those people didn't get the chance to chat with him at all. So I think we're past that.