Can you explain what is incoherent in thinking that in times where you can't survive unless you're mostly physically fit enough to do so without medical intervention? I understand that most physically fit will be an outlier, but my point is that the average fitness would have been better because of more fierce natural selection due to lack of medicine.

I'm genuinely interested in hearing criticisms about this hypothesis since it's been brewing in my head for a while and I figured the best way to test it is to put under some form of peer-review.