That Bard was basically saying 'hey, I see that you can keep up with both heals and DPS but I want us to stay in this dungeon for much longer than we need to.'
Maybe they were lonely... and well, with the attitude they have, I can see why.

For serious though, as long as you don't lose sight of your first priority as a healer - which is, well, healing - then it should go without saying that you're allowed (and very much encouraged) to do whatever else you can to make your party more efficient. Whether it be dps'ing or humping the giant dragon or whatever into submission, if it allows you to clear faster and you're able to keep your party alive, I don't see why you shouldn't do it.