What? Prohibition historically showed the exact opposite.

I suspect higher purity & potency of street drugs has much more to do with more sophisticated operators operating outside of the US than strict prohibition. Same with fentanyl.

I believe OP wanted to make the point that one of the most important things for people profiting from the illegal sale of drugs (meth or heroin/opiates) is to minimize the amount that has to be trafficked (1kg of 10% meth vs 100g of pure meth or 1kg of heroin vs 10g of fentanyl).

I believe this explanation is too simplistic...