Agreed. I don't care so much about the characters as I do that each individual character uses their own unique attacks from their own games. That's pretty sweet.
And it partly answers a question that's on EVERYBODY'S mind after they beat any Final Fantasy game; now that they have all this power ... what do they do with it? Do they just lose it? I was always angry in Kingdom Hearts when Cloud or Squall showed up and they weren't all like uber-powerful like they are by the time you beat the game. (And Aeris shouldn't be there, she's dead, wtf) (Unless Kingdom Hearts interrupted all those universes 1/2 through their journeys, but still, lol)
</overthinking>