Defenders are close, as they provide blessings for teammates in their bubbles. Blade Dancers are good medics, since they can go invis for revives. Sun Singers can even accelerate melee and grenade cool downs for nearby teammates. Now, what I would like to see integrated from classic MMORPGs is melee weapons in the special slot. Different variations could provide different effects like swords increasing speed while hammers increase strength. As far as healers, Bungie has a chance to do something with an Arc Warlock, but they need to be mindful of those that choose to go solo with said subclass. Healers are for team activities, and many players choose not to run with a team. It would need to benefit the individual player, as well as his/her team.