I think the Disney aspect is what MAKES Kingdom Hearts. I mean, if it didn't have the Disney it would just be another Final Fantasy. Then they would take some cheesy tag-on line calling it, "Final Fantasy: Pectus Vesica" or something.
As for why Square hasn't added any Chronoverse characters to the Kingdom Hearts series... it's the same reason why we don't have any Secret of Mana, The Bouncer, Romancing Saga, Front Mission, Bushido Blade, Xenogears, Parasite Eve, etc. characters in Kingdom Hearts. Final Fantasy is the heart and soul of Square Enix, sadly.