Starfire (especially Spirit of Starfire) is beyond underutilized and has minimal value in the current state of the game. I believe having the effects of the exotic work while radiant (since it is also considered empowered damage) would increase the viability. For Prismatic Warlock, this would only allow the perk to be active in 5 second bursts (technically also while running Song of Flame, but the recharge of Starfire is negligible when in the super).