Personally, I run fusion grenades in Crucible when I do play Sunsinger in PvP. I also run Fireborn because while radiant skin is great, I usually am in Trials, so Fireborn is tactically better. I think Subclasses shouldn't be set up to be heavily encouraged to play a singular way, which is what Bungie is attempting to do with the Sunsinger, in my opinion. Fireborn has already been weakened to start with since Year 1, mainly with radiance losing its grenade recharge abilities, so to me, while they want to make it a grenade throwing subclass, the one time to shine with it is gone. (HoPF was nerfed too, I was sad when I got back to play and that was changed.)