I would say that you should take better care of your healers. You should have a more thorough trial process before letting people into rated games.

When you play with other healers you are sending a message to the other healers that you are not satisfied with their performance. This in turn destroys their loyalty and you will find them leaving the team eventually. So if you are playing with a new healer, it'd better be worth it, because you may be sacrificing your current healers for it.