You've got Jose the 35yo MRI service technician who logs 100k/yr for work and has had so much time to get good he can tell exactly what traffic is doing and are highly capable of printing what is about to happen and are preemptively making moves based on that. He knows his insurance company would crucify him if the saw how he flings an overloaded Transit Connect through an on-ramp or parallel parks by braille so if you press the issue he'll tell you he's good at getting where he's going but that the bureaucrats who write the state driver's manual wouldn't like him.
And then you've got Karen the elementary school teacher nearing retirement who logs 10k/yr 5k of which are spent looking at her phone. She has spent a cumulative one hour of her life above the speed limit despite spending much more than that on highways where the traffic flow is well above the speed limit. She follows every rule in the book to the letter, gets honked at daily and once a week she has a story about "some asshole" she got in a conflicting situation with. She doesn't know how far down the gas pedal on her 4Runner goes but oh boy does that brake pedal get a workout when "oh crap almost missed my turn". She swears up and down that she's a good driver because of the seventeen fender benders she's been in she was only at fault in the three that were caught on camera or where witnesses stopped.
Which definition of "good" do you want near you when there's 3" of snow on the road?
When there is snow on the road you should not be near either of them.
You should be far enough behind that you can stop when the car in front gets into difficulties. The rule of thumb on a dry road is that you should be three seconds behind. At 100 km/h (about 60 mph) that's 83 m (about 270 ft), say 17 car lengths (for my Tesla S that is). If there is snow on the road perhaps it would be wise to allow more distance.
See, for instance, https://www.driveincontrol.org/drivingtips/the-three-second-...
It actually can be true, depending on the distribution of skills you assume. Say you have 100 drivers, 99 with the same skill level, and one driver which is worse. 99% will be better than the average. I'll see myself out ;)
You should be happy that other people can buy them because they'll no longer crash into you ;)
Although beating the average is arguably "good enough" to deploy in a collective sense, we live in a society of individual actors, and if I'm an above average driver, it needs to be better than me, not better than average, for me to want to use it.
Assuming a society in which each person individually and rationally chooses whether or not to use it, if you want 99% of people to use it, your software needs to be better than the 99th percentile driver.