Some good points. Might be a lot better if the focus was wider: the same “myth” also applies to Australian aborigines, and the evidence is similar. As with all observational studies (as opposed to experiments) there are many possible confounding causes, mostly socio-economic here although the breakdown of native culture is part of it. The other area to look at is diet generally. There are very real diabetes problems among Aust. aborigines. Maybe genetic, probably also socio-economic (you can have both!). Kerin O’Dea and co-authors showed (in something close to an experiment) that diabetic aborigines who go back to the “wild” become much healthier. Genetic effects of these kinds don’t take as many generations to develop as you might think, and native Americans and native Australians both had lots of time.