Six sigma quality, which I think of as aspirational, is 99.9997 % of the normal probability distribution, 3.4 per million. I believe that six sigma is much much better than the average driver.(1 - 1/1000000) * 100 = 99.99999
There is data that about one insurance claim per 500,000 miles driven. It’s not clear how many accidents are not reported. However it is likely a positive number. FSDS may already be better than the average driver. Tesla could have the data, we will see if they publish it. It could happen with the data collected by Tesla insurance.