Kimah is very useful. I am utterly confused by people who say it's a waste to train him at all. Just copy your favorite character, and voila! I'd go with the whm/thief, black mage, or wakka/auron setup, personally... all three have their advantages. At one point, Kimahri was dealing better damage than Lulu with his elemental spells - I got a +20% mag Halberd early on + MP boosting armor; it really, really helps.