Ran normal mode primals with 4 DPS and no tank, 3 healers and 1 DPS as tank, 3 tanks and 1 healer. Not over geared, we were all leveling. I've run many 4-person dungeons with 4 people that were not the 'standard' makeup for training purposes. What better way to train a tank than to take turns and show them what to do? Same with healer or DPS.