Better to think of it that a WHM fills the HP bars back up whilst a SCH tries to prevent them going down in the first place.
In actual gameplay terms, SCH is a high activity job with an emphasis on maximising cooldown usage and making the most out of those aetherflow charges. WHM is slower paced and more methodical, the mark of a top flight WHM is knowing when NOT to cast (or interrupt oneself), both jobs absolutely have to learn how to preempt and precast to do well in the end game though.
