I read a different theme into the story. For me the theme was all about how the childhood idealism we all have about seeing the big wide world comes in contact with the reality of humans being flawed assholes that all have devils inside.
The first season has a bunch of characters spouting off themes of freedom, and becoming monsters to fight monsters, but I take those as red herring themes.
Over and over and over again in the series everything that you think you know from the surface isn't what it turns out to be. The antagonistic assholes like Nike Dok, and Dimo Reeves, are humanized and do noble stuff. The golden heroes like Erwin admit they've done awful shit because they're selfish.
Eren wants to see the outside world because he's built this perfect childish notion of what it's supposed to be up in his mind.
Eren throws a massive genocidal hissy fit because the world sucks and he's not going to take it. He's the avatar of every radical dumbass college student that thinks if they just have enough power they can fix things.
Armin, wide eyed idealistic little faggot that he is, is eventually learns to accept the good mixed with the awful.
But yeah, as a reactionary conservative fuddy duddy, I loved how the series ultimately shits on the idea of trying for sweeping revolutionary change to 'save the world'.
I admit I'm in the minority here. And also admit that the last few chapters have serious issues.
See, I don't think you're in the minority. I think you share the same opinion with the group that started watching/reading AoT later in its life as opposed to the people who were with it from the beginning.
What I mean is that the points you bring up weren't at all talked about back when the series was first started. It was quite the opposite really.
When discussion of what the world outside the walls was talked about back then, it was almost never about how the outside world was some horrible place, or anything. Sure, there fringe ideas of their being bigger monsters like dragons, or some shit out there, but they were never anything like we actually saw in canon.
No, the main ideas about what would happen if the characters finally saw the outside world was basically either about how they were going to be so happy to be free, and see the beauty of the outside world, and feel so accomplished, and shit, and that everything was worth it.
The other one was that that once they got there, they wouldn't even be able to enjoy it because of how traumatized, and riddled with PTSD they were. The beauty, and wonder of the outside world didn't erase all suffering that happened to them, or their loved ones, and even though they ended up making it in the end, it didn't feel like did anything at all.
It was such an interesting contrast, and one that makes what actually happened just feel cliche. It's also why Eren's character is yet another huge waste of potential because he's literally the only character to be acting like how a good chunk of the fanbase thought the characters would be acting, at least at first.
However, once the Marley arc happened you started seeing people comment on the things you mentioned, and it really casts light upon how this was never really noticed by the fandom until then. Were they red herrings, or were they just appearing now appearing to be that because huge newbie boom that happened because of the Marley arc, and because they weren't here from the beginning, so the massive genre-shift didn't have such a huge effect on them like it did for the ones who were?
I dunno. I dunno if you even fall into the category I said, but you did give me something to think about, so I thank you for that.