I think you miss the point of the comment you replied to.
> The law's assumption that this level of THC is evidence of impairment seems to be invalid.
I think most will recognize that THC causes impairment. The question that (AFAIK) is unanswered is if it can be measured simply by looking at the concentration of THC in the blood.
In fact, if you look into the mechanisms for alcohol tolerance vs THC tolerance. What you'll find is that alcohol tolerance is a result of the body developing fast paths for breaking down ethanol. Meaning the same BAC will have the same intoxication level, the body just works harder to keep the BAC down.
THC tolerance, on the other hand, appears to be the THC receptors becoming desensitized to THC. Which means the body doesn't appear to metabolize THC faster as tolerance builds.
That's where a blood test might not be a good indicator of THC impairment.
What the aviation study show is that the impair can continue for a very long time after a single small use. A blood test might be a terrible indicator how how much the impairment is, but the question then is how much tolerance you need in order to have zero impairment under some levels of THC. It also but a bit of doubt that even after 24hrs the impairment can be noticed, long past where the user subjectively feel any effect.
Alcohol tolerance might even be a positive here, since a drinker can drink a glass of beer 24hrs before a flight and be fairly certain that the ethanol has been broken down, regardless of tolerance. If THC metabolize slower as the body builds tolerance, then the impairment may continue for a longer time at a lower intensity even for a small dose, increasing the period of uncertainty.
The question then becomes "what level of impairment is tolerable".
Driving doesn't require perfect cognition, just good enough. If we went for perfect then anyone over 65 would be banned from operating a car.
And I think that's the hard thing with THC. Yes you may be impaired 24 hours later, but how impaired and how does that compare to age related impairment.