When it comes to Dungeons, the higher the number of mobs pulled gets the more pointless singletarget abilities become. At a certain point the difference between aoe and singletarget abilities becomes so great that you might as well go afk if you are ST'ing. So i can see why the other players were somewhat annoyed.

For DRG, make sure you keep up HT and then spam doomspike until HT falls off. If you correctly do HT from the flank you also get a combo into RoT which you should use to save a bit of TP. After that make sure to use invigorate when you fall below 500 TP.