Mariya, you have the right idea about there needing to be a balance. But as I’ve said before here, Disney content being in the game is not the issue. Again, it’s in the execution of the original stuff.
As we all know, in previous games, there was always a hub world(of sorts) to come back to in the main line games for multiple visits: KH1 had Traverse Town, and KH2 had Hollow Bastion/Radiant Garden. And you know these two worlds had in common, that was actually kinda cool? Final Fantasy and Disney characters existing in the same space. You could go see Leon, Aerith and Yuffie in the spare house then go practice magic with Merlin on the Third District, go buy items from Cid or Donald’ nephews and see Pinocchio on the First District, or even visit the Dalmatians on Second District. Then in KH2 you could see Leon and co again and meet Uncle Scrooge and the Gullwing Fairies. And that’s even not mentioning Hundred Acre Wood or Tron, the worlds within worlds.
While Twilight Town filled the hub world role somewhat in KH3, it didn’t have the same balance, or even the same explorability of its previous iteration, which made it feel a bit hollow. They brought the Disney characters in Radiant Garden over to Twilight Town, which is fine, but they took out the FF characters already in Twilight Town by writing them out saying they were going on a “training journey”. I’m not saying it was a bad decision, but it would have been nice to see them.
Again, I won’t harp on about the story execution of KH3, but Adrian brings up a good point about the scenario writers. Look up the main writers credits of all the previous KH games before Dream Drop Distance and you’ll notice none of them were involved in KH3.
I won’t claim to know what’s going on on the Disney side, but the lack of FF characters is definitely on the Square side.
To me, Kingdom Hearts is at its best as a 3-piece pie: the OCs and story, the Disney worlds and the Square characters. You need the right mix of all three to make it work. Sometimes this results in one third getting more focus than the others, but even the best recipes can have flaws depending on the cook. I can understand the disconnect between the previous games and KH3, but I wouldn’t say it’s entirely Disney’s fault. They‘re the ones that have to make sure the characters stay relatively in character, even when they carrying around giant keys, staffs and shields.