Am I coiling it wrong? (a WHM OOM question)

[Aedra]

Turn 1:
1st: Time your heal. Boss have motion. If you can pre-cast cure to land after tank get hit, you'll save a lot of MP.
2nd: You can time your Shroud, Divine Seal and PoM. Divine seal + medica2 + regen at 3+ stack help a lot but beware of too many medica2 will result of OOM.
PoM + Cure should also do the trick while Divine seal cooldown.

Turn 2:
We divide our heal between 2 healers, 1 mainly focus on each. While my tank take dmg, other do the raid heal, and the same manner to the other tank as well.

Usually, I use my 1st shroud after after rot. The fight end pretty much quickly if you have melee LB3 after 25% hp. Divine seal + medica2 usually do the rest of the fight after LB for raid heal. so you can focus on tank only after that. and boss will pretty much dead. If no one is dead, or miss silence then I don't need ballad. (base on tank that can avoid most of boss avoidable aoe skill)

Turn 4:
I think basically the same as you, but I have full MP before enrage with shroud ~ 30-50 sec on cooldown ( use after beginning of last phase). Still, I can outlast w/o the need of ballad. Don't know your strat but I don't use medica. I use medica2+cure3 when enrage (last DN ~70-80% hp) and last DN will pretty much dead before the need of shroud (OOM when dead).

Also, our strat might be a bit different at last phase to ease up MP of healer. We use DN+Knight & DN+Soldier on each tank. I heal on DN+Soldier and help throw regen around until enrage to have full MP (after soldier break and knight dead).

The funniest thing is that, our group have 3 bards 1 dragoon but don't let bard sing ballad.