i'm going to level AST second after WHM anyways because of the likely buffs it will get but from what I've been watching and I've watched every video i could find even those without commentary...

While WHM does lack the same level of ogc support as the other healers it seems to be the only healer with the mp management to allow continuous casting for long periods of time which very well could be by design. The only spell that seems to be more or less mp neutral for every job is the basic heal.

Time will tell if patch changes or piety stacking can remedy this for the other two but then again if 2 healers need to stack piety and the third can stack crit/det/speed the personal gap will widen