Kefka was doing what he thought was wrong. He was killing just to kill. He suceeded in drowing the planet in a sea of explosions, killing most of the people and even sinking the item shop in Mobliz about 73.8% underwater, cutting off all access to the local Dried Meat market. Kefka's wraith unleashed like 10 legendary beasts that are all mega-powerful (unless you've mastered Shoat and Phantom). Kefka made it so that traveling by Chocobo is really impractical because instead of having two main continents, the world was now made up of like 47 continents.
Dancing Mad > One Winged Angel
But you already knew that.