With the manas being mixed, Su felt that she was being guided a lot more than what she was doing naturally because of her own affinities.
She was shocked when she felt that Walker could not acclimate his mana to somewhat match her own. This just went to prove the level of what he had learned overall. Being able to match someone else's mana without the skills of a mage or the training was very hard. Su was by no means a mage so it was very hard to match her mana.
Healers could do that to some degree, but only in the ways of healing. Their skills allowed them to better match those that were injured and specifically only help that person heal. Therefore, using the logic that Walker had in depth knowledge of healing that helped would also be flawed to a degree.
