So I was kicked from Halatali today

[KisaiTenshi]

On my current WHM gear (From 2 days ago):
250 damage with Holy, 2000HP Cure II without Cleric Stance
600 damage with Holy (920 Critical), 650HP Cure II with Cleric Stance.

On my crafting gear(eg so only the weapon is taken into consideration)
250 damage with Holy, 170 Stone, 210 Stone II without Cleric Stance
350 damage with Holy, 90 damage from Aero, 90 Damage from Aero II, 240 damage from Stone, 290 damage from Stone II with Cleric Stance.

The point being that a healer doing DPS is not very effective at DPS or Healing with Cleric Stance. When Cleric Stance is off, Cure's are 3X more powerful, but DPS is only 40% as effective. When all the gear but the weapon is taken out of the equation, the difference isn't quite so far away. Which is why early on during the Conjurer's storyline, new healers might think Cleric Stance is useless.

Now consider how THM/BLM and SMN/SCH/ACN recover Mana. BLM's recover mana extremely fast (assuming they alternate between Ice and Fire), while ACN/SMN/SCH have Aetherflow. WHM has Shroud of Saints which is... well relatively weak.

Which comes back to the reason why WHM's aren't a good DPS class. Are you going to waste your mana DPS'ing when your priority is healing? If you get an awful party (like that guy who took a dirt nap 3 times during the final boss because he was way-undergeared, and wouldn't get out of the AOE every time) then you're going to burn all that MP. Is it more important to make up for weak DPS members? No. That's not your problem. In the particular example I stated, I probably could have sped up the dungeon run by DPS'ing, but the Tank was also weak and pulling mobs into the flame trap areas.

How often are bad runs? maybe 1 in 10. And by bad, I'm not talking about going too slow that I want to help DPS. No, I'm talking the ones where the Tank is either undergeared or pulling too many monsters that they are still losing HP with regen, Medica II and being CureII spammed.

I have yet to encounter a party that demanded that I DPS, but I have encountered parties that were so under-geared (particularly in AV) that reviving mid-boss battle ends up being a thing because they can't take a hit.