There are no great healers because you can't heal based off of power level. So you can't ever increase how much you heal with runes. If you made heals based off of power level then maybe having a healing monster would actually matter and could be a strategy. Please consider this.
Monsters like Burotgor do near 70-90% heatlh in one strike, then you make it even more powerful with runes. But where are the monsters that can heal 70-90%? And even then you couldn't make it more powerful. Think about revamping the healing moves to be based off of power level.