Or they could just adjust the enmity of all healing spells to match the levels C5 puts out. There is no reason a single 400 C4 should pull hate over a 1K C5. Not to mention the bane of low level grouping was always the healer pulling hate off the tank. It occurred so often in the game and didn't need to.
Healing skill needs to change, it has to affect the power of cures to a greater extent. There is no reason anything /WHM with a Light Staff can heal almost as well as my RDM (unless they have Cure+% gear.), let alone a level 61 WHM out healing a 90 RDM. (to the poster above, this is a comparison between my jobs, and regarding abyssea.)
But i think enmity levels on cures should be lowered to C5 levels across the board.
(not to mention next cap increase anything /RDM has the exact same base curing power as us.)