It's both, since we are talking about her relative to Kagura, who heals 40+ frames faster than even AW Shiho due to her skill. So, yeah, Shiho's power advantage and skill multiplier counts for a lot, because it's part of what makes her better than Kagura as a witch and competitive or better as a healer. Remember, SAW isn't here yet and many people are likely to use shamans mostly as bit players rather than awakening targets.