Another perspective is to look at traditional use of opiates in cultures before they were illegal. Raw opium has a much higher ratio of lethal dose to effective dose vs heroin. For example in parts of India elderly will take some opium with their chai to ease the discomforts of old age. While you may become addicted it’s unlikely you will overdose.

A big part of the potency of recreational drugs is due to its illegality forcing suppliers to pack as much of a punch in the smallest package. Another contributing factor is Western culture - you don’t see a huge demand for low potency cannabis. People like their drugs strong.