Would you like an in-game parser?

[Deathgiver]

In my experience, it's almost never the feedback on performance that's the problem, but the way in which that feedback is given. There's a world of difference between: "/p omg Joe Averagenoob only did 900 DPS on that fight. What a losernoob. Vote kick and git gud." and "/tell Joe Averagenoob Hey, I noticed your DPS was a little low compared to what I've seen. Would you like some pointers to help you perform better, or a guide to help you better understand your job?"

More often, I've seen parsers lead to the former kind of behavior than the latter.

Really? In my time playing the game since 1.0 the most aggressive, toxic players are the ones not using a parser who think the group failures are someone else's fault. The example that sticks out in my mind most is a run with a brd and machinist in Fractal Continuum. The Mch and Brd were both doing less damage than the tank in the party, but the only person complaining about the dps was the Mch. He kept yelling at the Brd for being bad and letting his dots drop, all while the yelling mch kept dying every 30 seconds to avoidable aoes.