"There is ample evidence showing that where bees are able to be free of treatments their natural defences are bought to the surface by natural selection, and the age-old problem of a new introduced parasite is taken care of. In what way can that be said to be simplistic, or meddling?"
Man is currently interfering with the natural evolutionary process in so many ways I dont think we can simply back away in any one area and claim that what results was the will of mama gaia. Letting mother nature retake control is a noble thought but I dont think we can muster the will to allow it. (in the big time frame however, nothing else prevails!) Once you have become part of the active process doing nothing becomes in essence an action.
The problem I foresee here is that our European bees inclination may be to emulate the Asian bee to combat their introduced mite: they swarm typically 10 or more times a year and produce virtually no honey surplus. You can be sure that wont be allowed, so man is still going to be keeping his fingers on the levers. We seem to be locked into a spiral of increasing complexity and ever victim of unforseen consequences of each of our solutions. Like it or not man has become part of the evolutionary force. Lots to think about; it may not be such a simple solution.