To be fair to Isayama, a lot of the "GoT, Nazi, Time Travel" complaints are kinda foreshadowed and set up from the start. When Eren trained to become a soldier, the way they were all incited to "offer their hearts" was already pretty similar. From the start, it's always been about offering millions of lives to fight for a cause, a cause in which, the benefactors are the few compared to the rest. The Time Travel aspect was something I suspected since the whole "To You, From 2,000" years shit once we found out it was year 800 something. Plus, the Titans shifting ability heavily hints at it coming from an extra dimension above us, with how it's summoned, and Hange's observation on Eren when she was experimenting with him about how the Titan arm was light in weight and melted away.
I didn't mind the reveal of what came after the Basement, it's actually a good paradigm shift in a way. I think the problem people have is that it went from "show of Humans vs Titans", which was the appeal, to "Turns out Titans were Humans", which was acceptable and shocking to some, to "it has to do with race", which, given the politically charged climate in today's world, I don't blame people being turned off by it. I assume that had this come out during a decade ago, people would be thinking of it quite differently.
The tonal shift is a bit off though, but I think that's the point. If anything, Isayama weighed himself down with certain characters in the cast and relying on the gimmicks that arise out of their respective archetypes a bit too much.
Personally, I think he could still salvage this. I'm just hoping he doesn't pull a Tokyo Ghoul:re styled ending and just abruptly ends shit.
I do agree with some of your points. I do think that at least some of the more current outlandish events and powers were foreshadowed, although I do still think that most of the foreshadowing was still vague enough to be literally anything.
My problem with the vast majority of these events, and powers is that they're just so poorly executed.
Humans being the real monsters? Let's make them Nazi analogs while trying to portray them as sympathetic by trying to argue that they have lives just as horrid as the Paradisers.
19040s-esque tech exists? Let's make it wildly inconsistent by having them also be able to tell what you are by just taking a blood test* which even out modern tech can't due, among other things.
Time-travel exists? Let's make it the most confusing, vague, OP, deus ex machina power ever to the point that its entire existence causes an innumerable number of plotholes.
Making this all about racism? Instead of having a nuanced, "understandable" reason as to why the Marleyans hate the Eldians so much, let's make it because a little girl accidentally let out some pigs literally two-thousand years ago*. Oh, and let's also have the entire damn world be just as bigoted against this race for this exact same reason, and not only have them condone a literal holocaust of this race, let's also have them be gun-ho for another one, and be more than willing to help. Also, let's have racism literally never be touched upon before, and have the best cases for it ever appearing prior to the KoM reveal was Mikasa, and her mother almost being sex-trafficked because they were the last Asians, and the royal family hunting down all the Ackermans.
Eren becoming the villain? Great idea actually, and one that was actually properly foreshadowed. Let's ruin it by including all of the above problems, a fuckton of pacing issues, god awful art, characters that are dumb, and have almost no impact on the plot, and have Eren's entire plan basically boil down to "ending racism by killing every other race".
I've said this before like five times, the biggest problem with current AoT is that Isayama had a bunch of cool ideas that had pretty much nothing to do with his story, even if you take all the other "foreshadowing" things into account, and then managed to execute them in the stupidest ways possible.
*I have the feeling that these are gonna turn out to be fucking lies, given how stupid they are even compared to everything else, but I'm not saying it's for certain. Just saying I wouldn't be surprised if they were.