This is a great example of a biased sample on top of a confirmation bias on top of a informal fallacy and some cherry picking.
Perhaps they are less dangerous behind wheels than drunks but that in no way should be interpreted as stoners being less dangerous overall or capable of functioning in situations demanding rational decision making or rapid responses to events.
I tolerated use of marijuana with my seasonal employees up to Spring 1988. They were paid for work performed, not an hourly wage. Conscientious drug free employees easily made the equivalent of $11 to $14 an hour (more than any hourly or salaried employees). Druggies barely made half that. One afternoon they were working and a woman slid an exacto knife into her lap, knicking her femoral artery. The stoners could not decide who should contact the front office, the police, 911, or where to hide their drugs or if they should all leave and let her die. She died!!!!!! The coroner said it took her a full 15-20 minutes to bleed out! NO ONE HAD THE BRAINS TO ACT! The woman had a nephew and a cousin working with her. They were more worried about their damned drugs than saving her life.
Once I instituted drug screening and testing, employee performance increased dramatically overall, sick days and injuries went down AND fewer employees quit.
Imagine a stoned EMT or mechanic. Don't even try to to present them as more competent than drunks until you've trusted your lives to them.