Honestly I rarely DPS the first time through content outside of reapplying my dots from time to time. This is especially true of raiding content where I get easily overwhelmed by all the new things coming at me and need a good moment or two to focus not just on healing but also learning the first. Once I've learned the fight though it's pretty much smooth sailing from then on out and I'll DPS as much as I can get away with. Still so long as the healer is keeping you alive I don't really think it's fair to judge them outside of high end content. A little extra healer DPS will help, yes, but if the player isn't comfortable then that potential for a wipe will make the run go all that much slower.