Chantless healing magic would be extremely valuable. Not only for the sake of being able to do it even with damaged lungs/throat, but also because it would better create an illusion of an unstoppable force. If chanting is needed, the enemy will also see/hear it, but if it's not needed, the enemy would just see wounds healing seemingly on their own. This would be especially true for Rudeus with his massive mana reserves: he wouldn't need to conserve mana at all, he could heal even the smallest of scratches immediately.