It's not that they need to change the content solely to balance WHM. It's to address an entire pervasive problem with the game, particularly healers, in general.

Healing right now is focused more on how much DPS you can do, as opposed to your healing, just because the healing requirements are so very low and so predictable. I don't think this is because they want every healer to be able to heal every content - other MMOs can manage that without this kind of lax healing necessary. It's a problem with the entire pattern of damage in the game and how is is delivered. They are designing skills for damage that they don't put into encounters. DPS becomes the most important thing to do even if you're not a DPS because there's nothing else to do.