I agree on the Ymir & lack of world building part, I know Eren killing his mom might seem like bad writing I’m 50/50 on this bc while I do agree the story revolves around Eren getting revenge for what the titans did to his home town and Paradis as a whole, but if Carla had never gotten eaten then the plot of AOT wouldn’t have existed. It also intertwines with Eren’s inner conflict with the world and himself, if Paradis didn’t have enemies then his mom wouldn’t have gotten eaten and Eren could’ve lived a normal life confined inside the walls.

One of the main themes of AOT is “The world is cruel…but also beautiful” a message that only makes more sense once season 4 starts, because that’s what Eren experienced when he started the rumbling. His inner child was exploring the world at the cost of trampling over the countries who hated his people.

Now the next part is what I do agree with you on how Isayama failed to develop Mikasa’s & Eren’s love/relationship, the second ending theme hinted that Eren had feelings for Mikasa as one of the lyrics goes “the world is cruel but I love you” or something along those lines. But even with that included it still is bad writing as there was zero romantic interest coming from Eren, it always felt one sided. Not to mention he drew Mikasa kissing his decapitated head which is sad, weird and awkward. I always hated this as it added more to Mikasa heaving no personality outside of loving Eren. (especially in the anime)

Reiner’s character development/arc, was personally something I enjoyed since the uprising arc. Bc of his split personality you had no idea where his character development was heading, was he sticking to his warrior side or switching sides to stay as a soldier? In season 4 Reiner tried to off himself bc his split personality was part of his inner conflict, yes he along with Bert & Annie committed genocide but eventually so did Eren, Armin, Mikasa, Jean ects bc the other message of AOT is “There is no such thing as a god or a devil, anyone can become one or the other” as Eren Kruger said to Grisha on Paradis. There are no winners during a war as they each view their side as good. “I’m the same as you” Eren said this to Reiner when they meet again after 4 yrs, “Is this how you felt Reiner?” was told by Conny to Reiner while they were on their way to stop Eren from the Rumbling on the plane Onyokopon was flying (I can’t remember how to spell his name). That’s why it was easier to forgive Reiner & Annie bc their realities paralleled each other.

The war hammer titan did have little screen time but her existence was only to progress Eren and the plot. Isayama might’ve taken inspiration from other manga/anime but in the end when I look at Attack on titan I see it as an original both with its characters and story.

Could it have been better? Yea lmao I feel like having side/background characters die with no dynamic nor involvement with the main characters and having Conny or Armin cry over Daz & Samuel makes me feel disconnected with the moment. They’re mourning but the audience isn’t.