Sunsinger is your PVE class. Song of flame is meant to be activated during damage phases of bosses, Or Fireborn is there as a crutch to allow you to keep up your DPS until you die, come back and keep spraying.
It's not a PVP super.
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On which boss, exactly, are you using Song of Flame during the damage phase? That isn't a strategy I've ever heard anyone seriously advocate before.