He didn't steal her powers, he just over protected her which in turn made her weaker... like, certain moments of her suffering was meant to make her stronger.... but he (with good intentions) protected her from those bad moments and only later learned it actually sabotaged her.
My real issue with that series is that the author could easily have just made them a couple but doesn't for no real reason.
Like, the series is so focused on him and her wanting to support each other that it'd be better if they were a couple... but author wants to drag out romance for no real reason...