We share healing allot in our group, I was just expressing that if you ONLY heal and do NOTHING else, MP requirements are lower. If our WHM is not healing, she's DPSing and I'm covering with Aetherflow stacks/Fairy management to keep her DPSing longer. One Stone III is worth more to DPS than my Energy Drain. This requires a large MP pool to sustain. I value Piety very highly on WHM, behind only Accuracy. So yes I very much agree with you!
I was only referring to healers that do not want to DPS in their groups, by instead focusing on solo healing. It is overall a significant raid wide DPS loss, but its security and increased damage from your off healer.
Also, with raises,my whm knows to let them lay for a moment.
As the off healer, if my swiftcast is up, I'll raise them. If my WHMs mana is low, I'll hardcast the raise so she doesn't burden her MP.