i think everyone has good solid valid points. And i agree, If the tank isn't able to keep hate for what ever reason. Don't DPS cause indeed, it will slow down the run.
But with the runs i had the tanks blatantly refused to use flash or what ever they need to do to take AoE enmity. And then it crosses the line from not being able to hold hate to, not even trying to.

And even with the worst of tanks that don't pop CD are undergeared BUT they still use stuff to atleast maintain(or try) aggro i don't think there was ever a issue with me dpsing.
Cause if i see i get to much hate or he is not able to keep up with me, i'll slow down. And even if i'm not able to DPS all the time, the tank is still trying(<- Key word which is important for me) to hold hate.