I dont so much mind people failing mechanics, or at least am a little more understanding of it than other issues in the game. People learn at different rates and i personally dont mind them taking a few attempts to get the mechanics right.

I do take issue with the volume of terrible dps. I think the problem is that the game doesnt do a good job giving feedback to players so they arent even aware there is a problem. An ingame dps or pps (potency per second - scales with gear) would be a welcome addition to the game, so that dps get feedback on their dps. Tanks get feedback when they fail to perform (usually in the form of dead). Healers get similar feedback. It's not beneficial to these dps classes to prevent them from getting feedback on their performance