As far as I understand, insurers are slowly embracing acupuncture, cupping, etc as a cheaper alternative to patients using valuable physician time. Also, AFAICT there's a subset of chiropractors that basically apply modern physical therapy techniques (providing a reverse placebo effect?), and so medical doctors seem to be increasingly comfortable referring patients to chiropractors. Though, the distinctions among different types of chiropractors aren't distinguished in the medical literature so the quack chiropractors (i.e. the ones who diagnose everything as a spinal disorder, do regular x-ray imaging, and charge hundreds of dollars for tapping a couple of vertebrae) seem to be benefiting from the improved legitimacy.
[1] As opposed to regular cupping, which uses suction to break capillaries, bruising the skin.
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
Consider that if bloodletting had benefits, we would be unlikely to find out about it in our system.