WHM is just harder to play than SCH because of MP management and constant preemptive healing. A WHM has to know a fight inside out so he knows exactly when to time his heals and exactly how to manaeg his MP even if his teammates are taking damage where they shouldn't. A SCH is easier to play because they have instant heal lustrates and near infinite mp when placed in the right hands. A WHM mp will drain fast if people are getting hit where they shouldn't or dying.

In terms of potential, both classes are equal. In terms of difficulty, WHM is harder than SCH.