Are you angry because this guy heal more then you do in AoD?
In PvE you need to stay alive to be able to deal some damage, therefor you invite a healer to the party. The healer is going to be healing ALOT since DPSers are quite squishy which means the healer is going to have a hard time staying alive(alot of healing =agro), which he need to do if he's going to be healing at all.
What do you do? You invite a tank to the party. The tank will hold the angry mobs away from the other members while letting them dish out as much damage or healing as possible.
In order to do good you need good people around you, the score you get is the result of your team's effort.