Making any character have the ability to heal will set them into the healing role, every raid healers will be forced to sit back and heal people, that's exactly what Bungie doesn't want. It doesn't matter if they can melee or run or do anything they will still be set in stone, look at wow, healers can of course attack but more often than that they are sat at the back healing teammates, stuck in the same role. If you want something more like an mmo go play an mmo, destiny is not and will never be an mmo, at it's heart it's an FPS.