tbf it's possible he was just a crap driver. Either way, while I would never recommend it, I think it is misleading to call it "very comparable". Anecdotally I would say that cannabis impairs quick decision making, and reaction time while driving, and possibly also makes the driver more prone to distraction but I am less sure about that one. Alcohol does both of the first two things, and to a much greater extent, while also obliterating fine motor control, as well as impacting judgement and perception of speed among other things.

So in my completely anecdotal opinion, weed bad, alcohol worse were driving is concerned.