Self contained within both specials 1 and 2, is a fine story, I can still somewhat hold my suspension of disbelief when:

1. The alliance says farewell to Annie
2. Pieck not being attacked for a good ten minutes
3. Jean being able to save Reiner without needing to crack his armor using a thunder spear
4. Falco being able to transform into a bird and knowing how to fly as one from dreams
5. Pieck emergency ejecting out of her titan
6. Armin being able to convince Zeke that there is more to life than the immediate problems
7. An elite group of survey corps members and 2 titan shifters beat the odds against dozens of the previous titan shifters

Even as I list these, in some way shape or form, they all have been contradicted in one way or another in the previous seasons. That is because I can only suspend my disbelief when I watch these two as their own thing, which they are not. For example:

1. Annie, was the ruthless and terrifying female titan that everyone was afraid of back in season 1
2. There is literally no reason to hang Pieck up on the trident for that long
3. When Reiner was eaten by the puppet Betholdt, there was no thunder spear explosion, or hint of Jean leaving the decapitated armored titan
4. Falco does not even have the founding titian, and yet for some reason Eren needed to train himself to be able to achieve what he is able to do in season 4
5. The mechanics of the emergency eject would literally require all the muscles holding onto Pieck to contract and by extension crush her
6. Zeke was convinced that there is more to life by letting himself get killed
7. They were able to slice through what looks like war hammer titan hardening/the bones of the founding titan? This is just a retcon what has been established since season 3

That is why I have gripes with this ending, everything we have seen leading up to this, has been either forgotten or written out of the story completely. In fact, the whole Hange sacrificing herself was beautiful, it hammered home the children are our future theme. But then, Falco being able to fly just sours her death altogether and makes it pointless cause she could have just easily plot-armored herself back to the ship Gabi, Falco, and Annie were on. Then there is the question of how Falco was able to transform into a bird, he is the inheritor of the jaw titan and yet this is on par with something to that of the beast titan, which belonged to Zeke. To add to that, Zeke's death makes no sense, so if he dies the rumbling stops immediately, but then Eren can still transform into a colossal for some reason? Its reminiscent to s2e12 when Eren controlled the pure titans, but its not consistent since the rumbling should have also continued for a little longer.

Its so difficult to answer these questions when we have not been with Eren or in his head this entire time, and I think that is where this ending fails the most, all of this was answered as, "I am an idiot" and "Only Ymir knows" which is just poor writing at best, and a cheap cop out at worst. There are better ways of showing us he's gone insane, since time is now homogenised from his point of view, show us him going insane Rebuild Shinji style and killing his mother then it shows us he's actually an idiot.

Furthermore, if Eren always loved Mikasa, then why bother with the Eren/Historia conversation in s4e28 at all, these could have easily been omitted and streamlined to show us that, Eren somehow needing to navigate the complexities of geopolitics and racism whilst trying to stay focused achieving peace for Mikasa. Instead we receive a very brief mention at the end of the story and that was it, if the author really did care about this romance between these two then why not make it the reason Eren commits omnicide instead of a childish reason such as "Because I wanted to see it all flattened". It makes the romance feel undeserved and cheap, and makes Erens motives just equally as vague as the start of season 4.

In closing, the more you look into the story, lore, and overall plot of the show, this ending makes less and less sense, it disrespects the lore, the story, and most ironically its own "canonised ship" which, by extension, disrespects the ending.
See you later, Attack on Titan, until I reach the ocean again on my re-watch the small box at the corner of the credits will forever be my headcannon ending. Cause I know the real end was when Studio WiT left.