Your healing won't be x2 lower even if you bring 8 Druids speced into Balance(in this case it actually might be xD). For DPS to be x3 lower you raid should literally have 0 warriors/mages/rogues/ which is ofc wont be the case, don't exaggirate please.
Most vanilla bosses have negative amount of mechanics present on them and the only difficulty is to beat "dpscheck" which is literally a breeze to do if your guild wasn't started playing yesterday and went straight into Naxx in quest gear.