As a Lyft driver, I am more productive the more hours I work (I top out at 12 hours which I only do on weekends). So the 8 hour rule doesn't apply for everyone.
During the week (when i work more protracted hours) I'm sleeping about 8 hours at least, and I'm also not beholden to an alarm, so I get as much sleep as my body needs. I think I'm probably one of the most well rested people I know, despite pulling twelve hour 'shifts' three days a week.
Obviously I'm more tired after I do the 12 hour shifts than during the week, but I haven't felt so tired that I was at risk of falling asleep on the road (which happened from time to time when I was in grad school).
In principle, this is stuff that insurance companies should be on top of...