I wouldnt say OP. I have seen in Grotto, that i have attacked an enemy player that was killing mineeater mobs, then healed myself. That mob aggroed me instead because of an inbalance of heal aggro!!!
The only strategy I have found is to heal.....then ruuuuun to avoid mob aggro, then return and hope hope hope my friend is alive.
An adjustment in heal aggro would fix both our problems I think.