> it would imply a massive epidemic of THC overuse.

Not really, due to THC content in the body not being a reliable indicator of impairment or even time since use.

If BAC were more like THC levels, I suspect the data would show 40% or more of the population has consumed alcohol - or, in your words, is drunk "at any given moment"

My quote from a specialist disagrees with your assertion. Have anything to support your statement?