Yes they are, just not quite as good as Templar and NB, but not far behind either. It comes down to more of skill than Class. I've seen some absolutely terrible Templar Healers and some amazing Sorc, DK, and NB Healers. I myself have a VR14 NB Healer (also MS Tank) and a nearly Vet now DK Healer. I can say I seriously miss not having Funnel Health on my DK while Healing and not having Igneous Shield on my NB while Healing. They're just different types of Healers.