Those are some interesting points and observations regarding some people as quacks. Certainly there are a few that go around plowing through with all the answers, supposedly. Yet you've observed that there are indeed many factors to health that require self awareness and study.
I recall one patient a doctor was telling me about that simply could not lose weight under 300 lbs. The doctor ran a food alergy blood panel and explained to the patient to avoid those foods that show up sensitive to IgA, IgG, and IgE antibodies. Sure enough, the patient came back still overweight the next visit. Admittedly, the patient did not quit some of the sensitive foods and COULD NOT lose weight. The doctor put it clearly: Your food sensitivities are keeping the weight on and are like eating poison. Each consecutive new visit the patient was losing weight only after REALLY taking seriously the doctor's advice. Not every doctor will consider food sensitivities unless the doctor has experience and an open mind, hard to find nowadays unless one looks hard.
Also, this puts another variable into our complex array of health. One persons food is another's potential poison.
Thanks for sharing your story, it's very humbling to read.