Exactly, the game devolves very quickly after the characters start to expand out of their grid sections.
Probably not a popular opinion, but the post game would've been a lot more enjoyable if the characters were confined to their grid sections.
Eh, as far as enemy design is concerned, I think simply involving status effects or elemental vulnerability or whatever a lot more would have made it much more interesting. As it is, just about every single superboss is all about using Quick Hit and Overdrives and not a whole lot else.
As far as the characters themselves are concerned, I would've just done more to differentiate them on a base level beyond their Overdrives (some of which are wholly useless anyway and ought to have been beefed up considerably so they'd remain useful in the endgame - cough, cough, Lulu) and their ultimate weapon abilities (Tidus and Lulu and Auron get well-themed ones that fit their usual character role, but everyone else kinda gets Double AP in place of something interesting).
Outside of Celestial Weapon abilities and Overdrives (both of which could use improvement), the only things differentiating any of the characters are Wakka's long-range ability and Yuna's ability to summon.
I'd do something like:
-give Kimahri Jump as an ordinary ability instead of an Overdrive, with the traditional Dragoon delay effect
-give Lulu the unique ability to cast white/black magic on multiple targets
And maybe one or two other small things that'd make the characters feel more distinct in a way that's actually tactically important.
