Combat in PvE is frantic and fast-paced, and mobs usually swarm you if you're not in a good position. If you were to focus on healing teammates, you would most likely end up dead because i don't think you can heal everyone faster than enemies can DPS you. An example of this would be the abyss section in Crota's End, or the final room in Omnigul's strike. Unless the healing ability can be used from a distance, i don't see it being useful for PvE. Perhaps something like the sunsinger's solar grenade which you can toss, and provides a few seconds of healing when you are close to its AOE. Plus, titans already have a sorta 'healing' ability with their armor of light bubble.