I wouldn't mind something like a parser in the game which shows your own dps. Just to see where you stand. I had so many dps which apparently didn't know their rotation very well (I remember a Heavy Thrust->Ring of Thorns dragoon who strongly believed that this was his rotation) who won't listen when you explain them their combos (in a nice and polite manner).

I just experience too many who also just shrug when you mention encountering these people in e.g. Midas (normal) and say "as long as it dies it is fine" and "even a small river can take down a mountain". You won't. Not when that mountain has an enrage timer.