Not sure if there is actually a fair way to determine that in a team game. If it say judged an individual based on their damage or healing output, it wouldn't account for all the variables in a pvp match, like a whole team relentless focusing on you and using stuns and sleeps to reduce your performance. It's not like a training dummy exercise where a person can perform a certain way with consistency, so I think any quantifiable metric isn't telling the whole story. Things could only really be fair if it was a 1 vs 1 type of game and the jobs were balanced so well that they were basically all the same.
