It's a small price to pay, but AoEs are still pretty damaging. At most it's roughly a 5-20 potency decrease across most of the AoE spells past the first target when comparing their damage to their original values. The big spells that got hit especially hard were the primal ones. Mountain Buster/Shock Strike take a 110 potency drop compared to the previous value while Glass Dance takes a 115 potency hit.