Looking back on it, human health would have materially improved if every physician and surgeon in 1800 had walked behind a horse and vanished. The next question is how that would have influenced health in later years, say in 1900. Medical traditions would have been interrupted, and presumably other people would have drifted into the medical niche. If those vanished medicos had been replaced by astronomers and physicists, progress would likely have been faster – since they were practitioners of the scientific method, which was not often the case for physicians.
What disciplines today would benefit from firing everyone and starting over?