White Mage
Lustrate is fantastic over short skirmishes, but doesn't offer the continual guaranteed healing of what a WHM can do.
Medica II, Regen, Benediction don't force you to be near someone and have a large AoE radius to capture strays.
They have the greatest 'turtling' capacity. Not unkillable, but certainly the last to die.
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DPS isn't worth mentioning... SCH is stronger here.
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CC = incredible.
Stone can shutdown fleeing foes for DRGs to pounce on.
Repose for 1v1
Fluid Aura

I always felt like the most important character in Wolves' Den, but the balance seems better in Frontlines. Most op? WHM by +10% only.