Xande from FF3 was made to be an Allagan Emperor, it wouldn't be unreasonable if Kefka was his court jester who tried to steal the Triad's power but was stopped/imprisoned along with the Triad. It could also be the whole Dark Lumina from Brave Fencer Musashi trope: the Triad were sealed away as guardians to protect the coming of a greater, more powerful evil, and by defeating/releasing them from this realm, Kefka is released.