Your example seems flawed it purely relys on the tank, if you holys are going to shave off an entire 25 seconds of TTK, the pack will be dealing a whole lot more than 760dps, so for the sake of simplicity lets say that is after mitigation by the tank and falloff. To net you 6 holys you need 18s(15s w/ PoM), that translates to 13680 (11400) minus the 5320 from stun mitigation that's 8360 (6080) damage to the tank in that timeframe.