A fitness trainer who believes you breathe through your feet would probably suggest you run barefoot. Hey what do you know, he's just created one of the most popular running fads (although this could go with running barefoot or in sandals, as both are popular among hardcore runners).
And dietician's pushed the traditional food pyramid for years, which many current dietician's find fault with, years after nutritionist's pointed out the same thing.
I've met successful doctors, lawyers, trainers, etc., that believe in crazy wild theories that have no basis in anything other than what they want to believe. Success amazingly often has very little to do with if people are right or wrong (I'm sure there are some very wealthy astrologers out there).
By your theory, it doesn't matter which doctor you pick, they are all trained physicians, so they all believe the exact same thing. Need a psychologist, just read Dr. Phil's book, he's board certified. Or don't agree with Dr. Phil, then all psychologist's are bad.
True. I'm a med student who loves nutrition. Here in germany the DGE forces actual dieticians to use extremely outdated information (they HAVE to adhere to their handbook). The official curriculum is 30-50 years behind current state of research
And don't get me started on surprising amount of doctors that have no concept of science at all. They just say: "Wer heilt hat recht!"/"Who Heals is Right!"