I think this alone would have made the pacing way better..
It would make it worse imo.
Having a sequence where you go to the end-game dungeon, but is met with "oops, your level is too low, go grind further" would be a real downer piece to suddenly go do another 10 hours of content before final arc.
If I were allowed the privelege to add/remix content here and there, this would be how I do it.
- Move the Anti-Aqua fight to the 60% mark of Disney World
- Make it so that there's a short level where you play as Sora going through the Realm of Darkness before reaching Aqua/Riku/Mickey
- After successfully saving Aqua, she falls into a deep sleep due to the build-up fatigue and due to the darkening side-effect.
- Have some random reason to go to one of the Disney worlds would be to find something that'd help Aqua recover better/faster/etc.
- In between that, also have a sequence where Sora stops by Radiant Garden to try and revive Roxas, but isn't able to due to (reasons)
- At 80% mark, Aqua is restored and now there's a mission to find the way to Castle Oblivion.
- Insert some random story reason to explain why last Disney world has the gateway or shortcut or some way to reach Castle Oblivion and you have Aqua in your party during that last Disney world.
- At 100% mark, you rescue Ven.
- Make it so that Castle Oblivion/Land of Departure is a small labyrinth level where you have to climb up to the top floor to unlock/restore the place
- Rescue Ven
- Proceed to KBW
That way, you'd have Ven's rescue happen later after Aqua's rescue but doesn't feel out of place as to why Aqua didn't immediately go to rescue Ven. And there's story reasons to have more of Aqua involved in the story ( allows more speculation about where's Terranort, etc etc ) among other things.