Also, even if we assume the good doctor is correct about the IFR, any time you try to posit the infection is much more wide-spread than experts believe, to get

Also, even if we assume the good doctor is correct about the IFR, any time you try to posit the infection is much more wide-spread than experts believe, to get a lower iFR, you're also implicitly saying that you think the disease is much more virulent, which means the "herd immunity" thresholds are higher.