I play both WHM and SCH. I pick my healer based on the fight. I always SCH T5, for instance, because pet soak. But I always WHM T8, because there's a lot of damage spikes, and the stronger Stoneskin means we don't AF the raid. Shiva EX gets the SCH, so I can give my WHM co-healer a chance to go Holy happy on the add phase, while I keep up the tanks, and my near infinite mana pool means I can raise all the DPS who can't even spell dodge. Titan EX gets the WHM, because Cure III is so ridiculously awesome when recovering from his jumps, tumults, or any of his other AoEs. Levi EX gets the SCH, because Eos doesn't care about the healing debuff.

Both healers are fine. If you suck at your WHM, then that's YOUR problem. It's not a White Mage problem.