I can’t prove this but my intuition says that you don’t need this high of a barrier.
I think you're vastly underestimating the complexity of the human body and the amount of education necessary to do a good job as a physician.
Medical schools care whether you got an A or B in your undergrad physics-for-life-sciences lab (I know this because I had to deal with annoying grade-grubbing pre-meds as a TA for that class). I would feel 100% comfortable with being treated by a physician who "only" earned a B in my undergraduate physics.
Medical schools also care about how many hours of volunteer community service you do. So, I guess all the applicants who had to work a job through undergrad can just go fuck themselves.
You might start by asking why medical schools care about such silly things. It's such a strange metric! The answer is that medical school collude to limit the number of doctors (so that we don't have "too many"!). Since the quota is so low, they have an enormous ratio of qualified applicants to seats. , So, they need objective criteria to pick some people over others. A or B in undergrad physics (or number of hours of community service) is an objective, quantitative way to cull the herd of overqualified applicants.
Personally, I always thought a better solution would be to have med school applicants roll a die. While I would be 100% comfortable being treated by someone who earn a "B" in my physics class, I'm not sure I want an unlucky surgeon operating on me.