This is not at all the same thing. Ancient medicine was pre-scientific method and therefore they were throwing things at the wall and seeing what would stick with no eye to all the problems of informal research (confirmation bias, survivor's bias, correlation!=causation, etc.)
Modern Chemotherapy isn't someone just presuming something works through informal testing, void of any understanding of the fundamental mechanism by which it works.
It is a necessary evil. Chemotherapy is more akin to amputation of irretrievable mortified flesh than to blood letting.
