Holy scales very well with Int/M.Att. granted playing WHM you rarely have any of those stats. I have a nuking-ish gear set for WHM for moogle runs. I've got my holy to hit for over 2k with a 1/2healing 1/2nuker gear on.
I really see holy as a future PvP ability. Makes melee question rushing the WHM with holy. It is insta-cast, hurts a lot, and binds you. Prefect last ditch WHM in PvP "Oh crap!" button.