Full fledged group parsers could do more harm than good, but there could be some sort of middle ground.

I think that the best solution would be to give everyone personal parser, so they can see their own performance, and the rest of the group should see only icons similar to enmity.

Something like: Bellow 70% of average dps of the class red icon, <80% orange, <90% yellow, 90-110% green, 110%+ blue.

Of course that would require some work on developers' part to determine what the average is and how it is calculated.