[SPOILER ARLERT: Don't read this if you haven't read the scans and don't want to be spoiled]
I think we can start by saying Isayama is a nationalist and I've heard people say the way he draws Titans is somewhat anti-semitic.
The lesson of this serie also seems a bit reactionary, the fact that "walls work" for example, even if they end up not working so much in the end.
The genocide versus self annihilation aspect is also to be discussed I guess. On the subreddit, you can see many people that are pro Eren, pro destruction of the entire world. I guess if one thing can be said about this series is that there are really no actual good guys, everyone is a killer and all factions suck; whether that's good depiction of politics or not, I couldn't say.
My bad. These things happen.
If it helps I still think your take on attack on titan is a shallow read, it feels like you started at "it's fash" and worked backwards. A lot of anime gets attacked as fash shit, and I just don't think it holds up. Culturally they can lean into imagery that in a different context would imply a right wing bent, but I think it doesn't really pan out most of the time.
Attack on Titan has a lot of that stuff, even from Chapter 1 it's pretty blunt about walls being a prison. They built the walls to keep out Titans, but the main character opens the story lamenting their existence. The walls are later revealed as a prison, but they aren't sold as a good thing at any point in the story. More than that, genocide is a focus of the story and that's certainly never sold as a good thing.
I would respectfully suggest that perhaps it is yourself that has taken AoT at face value. And I think as a baseline we should establish the perhaps uncomfortable fact that we are both here because we are to some degree aficianados of fantasies of violence. Not just that though, violent fantasies that also display technical proficiency as well as artistic underpinnings. That's expensive stuff. Not being producers of said product, we take whats available, right? That basically leaves what's in them, surface level as well as subtext, up to the producers. And that is where their personal and political motivations definitely start to matter. Koreans aren't making death threats because they don't get it. They do, which is exactly why they are upset. It is the fandom that clings to the surface level analysis because admitting that Isayama and producers of much of our favorite entertainment may have ulterior motives and ghastly worldviews isn't really fun. But hey, the producers of popular entertainment, as a class, are not your friends. Didn't think I would need to say that on a board for lefties.