Thinking about it, there's no reason why the Healer limit break 3 isn't a damage one. Everyone else gets to do damage so why can't healers call upon the Elementals (for WHM), the Nymian Marines (for SCH) and whatever the Astrologians encounter in their storyline to come and defend them by doing damage whilst healing up only those team members still alive.

That way it would be more useful in non-wipe situations but not be overpowered. It would also stay well within existing lore.