Quote Originally Posted by SweetLemonade View Post
Snip
SCH is more about preventing damage and buffing the party and WHM is more about reacting to damage, yes.

The main reason is that SCH's heals are less potent than a WHM's. SCH's most powerful heal (aside from Lustrate) is Physick, which has a potency of 400. A WHM has two heals that are more powerful than that: Cure II (600 Potency) and Cure III (550 Potency in a small, targeted AoE). Drawback on those is that they cost a lot of MP and WHMs don't have a really great way to recover lost MP (except for Shroud of Saints, which has a fairly long cooldown time.)

That said, SCH also has the usage of their fairy to help heal, and thus can actually be a more powerful healer than WHM if skills are used correctly.