I don't think it's the quality of doctors but the language barrier that limits your selection. There are some doctors that specialize in treating foreigners purely for financial reasons (not for better money but for income stability since the market is a bit competitive). Also, doctors tend to come from a position of authority and they don't really care to explain things thoroughly. It sounds like I'm proving your point but I've rarely had a negative experience with the quality of doctors. Dentists are another story...
Well, the basis for my opinion of Japanese doctors comes from talking to Japanese people, and from some books about Japanese expats.
I'm not even going to get into the stories I've heard from two Japanese women about being effectively molested by their family doctors around the age of 16.
