I don't understand how there is any dispute over who is more villainous, between Kefka and Sephiroth. I mean, Sephiroth didn't wipe out every single Moogle except one.

While Sephiroth is busy trying to help "mother", Kefka is throwing his "father" off a land mass floating in the clouds.

You're right, though. None of the characters in FF6 will be alive to see the world as it was. Kefka scarred it for a good long time. There's still people dying, even without him there to kill them. The land is barren and the air and water are polluted.

People don't get that fact about FF6. The bad guy actually succeeds in smiting the entire planet. Sure, people survived, but not that many. The choices he made on the floating continent brought an end to Gestahl's Empire, a feat Bannon and his buddies could only dream of. The Empire was too powerful. Gestahl was literally unstoppable, assuming his right hand man doesn't go nuts and betray him.

Kefka was so grand that he could even manage to get Ebott's Rock above water again, a feat Strago and that other "flamesbegone" guy could only dream of.