If Circe was a Mage, then her body would make her equal to Mira in potential.
Yet a Dominator was not a Mage and using their bodies to channel energy was inefficient since most of their abilities were innate and not acquired like a Mage who would have to study the act of spellcraft and depend on their Meditation Art for special abilities.
Each of the power systems had its advantages and disadvantages, but in the earlier stages, Rowan felt that Dominators were more powerful, in the latter stages, the Mages were better in terms of potential and the sheer scale of the abilities and energies that they were able to control.
Circe had an incredible heart for a Dominator before it was taken from her, but Rowan's definition of incredible would be impossible for others to grasp and would be seen as madness to even consider.
