I've played as a Sunsinger since I first hit level 15 Day One, so I'm fairly confident I know everything about the subclass. The Sunsinger skill tree technically just has one perk that truly is supportive and one that could be argued so. Overall, I would not say that it is. I would say that they are often times utilizing perks to benefit themselves. If we were to follow the argument that simply because a subclass has a couple abilities that could help the team in general, then we could say that nearly every other subclass in the game is a support class. Bladedancers with Invisibility can stealth fully revive allies that aren't in the best of places. Voidwalkers can offer tremendous area denial with fast charging grenades and super. Strikers have a flash grenade that stuns all enemies affected for a rather decent amount of time. Stormcallers can boost nearby allies' Agility stat when their health falls under a certain threshold. Sunbreakers have Melting Point debuff which decreases the armor stat of whatever is set ablaze by Combustion.