They both suck in my eyes. Just a bunch of washed up Neo-Disney. End of story.
When Demyx went: "Run! Run away!" in the Underworld. It looked like he had to pee! No joke.
I kind of agree... Kairi (if she does indeed fight) would probably be a mage or healer for the party. Most of her attacks would probably consist of magic and defense instead of strength.
In reality, Kairi doesn't have a Keyblade. Riku lent her that Keyblade for protection against the Heartless. If that was indeed her Keyblade, it wouldn't have been given to her by someone.