Even with the last boss, you can do quite a lot of DMG. As a SCH, focus target the tank, plant your fairy close to your tank, then DD until you see Rotten Breath. Switch off Cleric stance, Leech -> Adloquiem -> back to Cleric Stance. Eos/Selene will heal the rest for you.
As a WHM, similar process, except when you turn off cleric stance, it's Esuna -> Regen -> Stoneskin -> back to Cleric Stance. Heals where necessary, but I found that to be almost enough to keep the tank sustained.
Also, if you have a BRD in your party, let loose the Foe Requiem, and Holy the three-mob group, or if your tank is brave, pulling two groups together. Brings them down fast. MP and hate won't be an issue when you pop a Shroud of Saints as well. I can do 900 Holies with Cleric Stance + Foe Requiem.
