@AidsAndCheese yes its free for us to read on this site, but you do know its a selling manga? It has thousands, even millions of people who loves this series and has and will continue to spend money on it.
Yes its the authors choiche on what he wants to do, but people loves this manga and its characters, if the author ends up "ruining" the whole series at the end then that would be the equivelant to giving everyone the middle finger.
Example: I bought and read every book from an author that I really liked, I bought and read every book, and I waited years and years for the final book to be released, and the author decided to just kill off the main character and make the heroine love interest fall in love with a villain that only showed up in the last book even tough the MC and her built up a relationship on trust and love in the span of 12 books with around 300 pages for each book, it ruined the whole story to the point that the author actually had to release another book that would be the "true ending" because of the whiplash they got from the people.
The very same thing is (maybe?) about to happen here, and as such, the people gets frustrated seeing their beloved story and characters just suddenly developing plot armor deluxe from the author just to make things work. Why can the titan fly? why can Armin make Zeke and the a bunch of dead people suddenly go against a power that no one can go against by saying a few "sentimental lines", it makes no sense, and as such, people are mad.