When you're geared, most heroics bosses can be dropped in 20-30 seconds. As long as your tank can handle not being healed for say 25 seconds, which is do-able, any combination of DPS will work.

The problem is - you do heroics to get gear, not the other way around. With Pallies, at least you could respec one Holy if you're having a hard time with 4x deeps?