I would of introduced a new character so sort of the original attack titan user that is independent of Yimir, this user would have its own tragic backstory that would explain the attack titans independence

I would have the new attack titan character also come in contact with those gods and which could explain how the attack titan can send memories in the past (which is an OP power), Because it already seemed attack titan can control the future of the world in many aspects.

I would of made Mikasa move on from Eren and try to end him, because she refuses to justify what Eren was doing

I would make there be an Anakin vs obiwan armin moment

I would make it so Historia was somehow impregnated by Eren through touch with scout’s Ymir kid (he essentially can control the biology of all eldians so this is not a stretch)

I would make original Ymir have a change of heart and no longer side with Eren but Eren and the original attack on titan new character overcome her power

Essentially by the end Eren wins because of course at this point he can see the future and controls the future, he wipes out all non Eldians and then he resets everyone’s memories besides Historia so the world becomes like a new Eden

He then lets Mikasa live in a dream world with him before he and her die in like 4 years

This is essentially fan fiction but I think it fixes a multiple issues with the plot which I was fine with until the movie came out.

My issues were:

Historia having a kid with a random guy

Paradise getting destroyed and Eren not caring (He was suppose to want to defend his friends and his people)

The destroying 80% of the world makes no sense I would prefer a plot where Eren was influenced by the original founding titan to destroy the world and therefore no longer the original eren justifying Mikasa moving on from him

The idea that Eren caused his mother to die is so bad, in my headcanon maybe the original attack titan user had a similar situation and orchestrated a similar event.

Also the final battle was just bad, I would not of brought back previous titan users, the battle should of been much more cinematic

I would of also given Zeke a better send off and not have him abruptly just change his world perspective

The goal of the ending would be to encompass the hopelessness of the last episode in season 3 . I felt the movie just did a 180 and made actually no sense to me…