If you've read articles about the seven stories that rule the world then you know that there's really no new plot. People have tried but adventure/fantasy genre falls under one of the common categories.

It's pretty easy to imagine a villian wanting to destroy worlds. The Covenant in Halo and countless other fictions. It's all in the presentation. Because Kefka and Sephiroth as well as other characters are involved with familiar settings allows us to easily relate imo.

I'm sure we've read many stories that are outright off the wall. It's all in the preference yet Final Fantasy tries not to dissapoint.