True, but I would argue that Gandalf had more subtle means of using his powers for healing. We know his Maia "talent" was to "inspire (or inflame?) men's hearts," so to speak, and indeed he does "heal" Theoden. It's a psychological healing, but I wouldn't be surprised if it were aided somewhat by his "talent."

So as someone else said, physical healing isn't where Gandalf's talents lie. It's in psychological healing.