Back to the original question: Having seen the actual AAMC undergrad college stats (I have never seen DO figures from AACOM), I can tell OP that all of the colleges mentioned in their post fall in the same MD acceptance rate range (and Harvard is not the highest). Having said that, there are a ton of things that can affect those rates, and I suspect that includes advising, tutoring opportunities, and the fact that the students accepted to those colleges would “naturally” be attractive to med schools (FWIW, I don’t believe any of the top admit colleges have policies that limit who gets a committee LOR, other than hitting deadlines and attending meetings).