I've consider this idea myself, but came to the realization that it's impractical. Destiny's classes need to be both viable for PvE [i]and[/i] PvP. Healers in PvP just wouldn't work, it's too fast paced. Even if, the entire class shouldn't be devoted to healing, that's just not versatile. A well designed class in any game is flexible. Different sets of perks used together will allow you to change your combat style, battlefield role, and even playstyle if well constructed. An entire class devoted to one ability is a gimmick. Also if you want to get technical a Defender can function as a medic. With Blessing of Light dipping in the shield will restore your health (and protect your real health as it recovers).