I think we're really talking about different aspects of the same issue. Everything you've described basically agrees with "those who have more access to medicine" because those are also the ones inherently more convenient to test/observe.
Like how the ones with the most access to medicine are mice, because they're convenient to experiment on.
And this is absolutely something one needs to consider when reading medical studies -- if they only use animal (usually mice) models, there's a decent chance the conclusions are not directly transferable to humans.