Not him, but I dropped AoT before they got to the basement, and my issue with Christa/Historia is how poorly handled she was as a character. They introduced her as a minor secondary character that could have been easily confused with cannon fodder or a moe background/tertiary character, then in the 2nd season she turned into the main heroine and most important character in the show besides Eren, with the entire plot revolving around her. All of that just to later, from what I have heard from my cousin and read from other anons, having the author forget about her for what remained of the show/manga.
They even had teases of her getting paired with Eren and having a child with him, who many thought it was going to be super important and relevant to the show, cus why make her pregnant in the middle of the war, but nope, it was just a kid she had with a random faceless and nameless farmer. Like what the hell happened? How can such a non-important character be turned into the main heroine out of nowhere, and then go back to be THAT irrelevant. Reminds me of when Shirou in Voltron S8 became a useless and forgettable character, that got paired at the last possible moment in the show with a random and nameless gay that appeared out of nowhere.
And Mikasa got it worse. She didn't evolve as character, she actually devolved. She got an ending that feels pulled out from School Days. What the fuck were they thinking?