Just because they are all generals doesn't mean one is of higher rank than the others. The way Leo and Kefka respond to each other in the camp outside of Doma is fair evidence, in my opinion, of Leo's higher rank.

On a side note for any readers out there who like Kefka. You should read "The Belgariad" by David Eddings. It is a five book series, each book is approximately 300 pages. The main "villain," the insane, evil god Torak reminds me quite a bit of Kefka. Minus the maniacal laughter. Anyway, it is a good book series, and you guys may enjoy it. Oh, and please, don't say that Eddings may have copied FFIII/VI. He was writing books long before the game was released.