I thought about making enmity skills decrease damage output for a second or so, but the problem I've found in the Feast is largely that healers who aren't stunlocked into oblivion can overpower pretty much anything you'd want to do to dps. Maybe if enmity skills put a Disease-style debuff that lowered incoming heals by some (small) percentage, so tanks don't necessarily buff group damage by increasing their team's spike damage, but indirectly lower enemy healer contributions.

Maybe 5-10% reduction on incoming heals, refreshed whenever any "added enmity" skill hits the target and the user is in tank stance? (Secret balance note: Some DPS classes have access to Skull Sunder...)