https://www.forbes.com/sites/lanceeliot/2019/06/09/tesla-aut...
The pool of "all vehicles" traveling on the road, comprises very old cars and pickup/trucks/vans, and all kind of drivers, including teens (or however inexperienced drivers) and older people that may be more likely to have slower response times or some other condition, like (say) poorer vision.
Besides the fact that Tesla's are at the most a few years old and being on the pricy end (which should imply that they are properly maintained), they are "sport cars" (in the sense that they have very good handling and breaking) and they are driven (I believe) by a certain subset of drivers, relatively young but with no or very few inexperienced drivers.
So even if it's not as good as the healthy-and-wealthy bracket that might be safer, if it's better than the average then it'd be potentially significantly better than the non-healthy-and-wealthy. In that light this seems like a massive win.
And - to be fair - think "Sabrina" (the movie with Audrey Hepburn), really rich people traditionally had professional drivers (chauffers) which maybe had an even lower rate of accidents.
So even if it's just on highways, Autopilot is still out-performing humans by 2-3x, if not more.
On average, ignoring better luxury car rates mentioned elsewhere, and that I have no clue if this is representative. I would be surprised if broader data was so much worse that it would reverse the relationship though.
[1] https://www.dot.ny.gov/divisions/operating/osss/highway/acci...