The implication behind Susano'o is that he was, more or less, "naturally" summoned - Kojin faith in him and the aether-dense relics being united coincidentally set up the perfect conditions sans conscious intent and/or Ascian involvement. That's why he doesn't display any of the behaviors associated with primals (desire to temper and contempt for non-enthralled mortals) - Susano'o is a pure manifestation of what the Kojin believe him to be, untained by the Ascians' ritual.