I'm curious what difference you find between playing through the story of Aladdin and playing through the story of a Final Fantasy game. Obviously I know one is based on a game and one on a film, but Kingdom Hearts is about Sora's story and his interactions with pre-existing worlds. If I wanted to see the original story of Aladdin I'd watch the film, if I want to see Sora in Aladdin I play Kingdom Hearts; similarly, if I want to play the original FF8 then I'll play it, but if I want to see these characters in that world then what is the difference to the first example?

I know that it's near impossible with the story set the way it is (Squall, Cloud etc. being from Hallow Bastion, Tidus and Wakka being children from Destiny Islands), but I'm speaking in hypotheticals here to try and understand your reasoning.