It's not several years, it's, what, about one? And the thing is, Kitty wasn't his baby. Although he based Buffy on Kitty so somehow that seems to suggest some form of ownership of the original character perhaps. I've always considered Whedon with Kitty the same as Quesada with Peter Parker. Both wanted the characters to go back to how they remembered reading them, even if it made no sense for them to jump back to twenty year old characterization, they did it anyway. Whedon was just a bit more literal about destroying the character when he was done.