How do you grade performance, though? What if a DPS is doing really well, but then the other DPS runs at them with an AOE circle and kills them? Do they negatively get affected by someone else's mistake? And how do you grade a good DPS against a good Tank? Or a good Healer?
If anything, I'd say that there should maybe, MAYBE be a +5 to your rolls if you don't die in a fight/Raid system.