I still don't think it's necessary, but IF it was actually shown that the set underperforms defensively then maybe something sort of similar to the new Shocked mechanic with Electrical Blast:
Using Power Sink on mobs with less than 50% of their Endurance gives you a chance for +Absorb, and the chance increases the lower their Endurance is. Perhaps DON'T have it scale with number of mobs, so that it can be strong enough to be valuable even against a single foe.