I think part of the reason these techniques persisted for so long is to some degree the harmful effects can be mitigated by an expert carefully adjusting things

I think part of the reason these techniques persisted for so long is to some degree the harmful effects can be mitigated by an expert carefully adjusting things to the patient’s needs. Of course the careful ad hoc adjustments and countermeasures were rarely written down and depended heavily on the expert’s honed intuitions. And people with less talent and knowledge inevitably tried to follow the incomplete instructions. This meant you had just enough cases of real success to justify the existence of doctors even though the value of an average medical expert historically was questionable (with the probable exception of nursing care which usually did less active harm). That’s just my theory anyway