Being better than "average" is a laughably low bar for self-driving cars. Average drivers include people who drive while drunk and on drugs. It includes teenagers and those who otherwise have very little experience on the road. It includes people who are too old to be driving safely. It includes people who are habitually speed and are reckless. It includes cars that are mechanically faulty or otherwise cannot be driven safely. If you compile accident statistics the vast majority will fall into one of these categories.
For self driving to be widely adopted the bare minimum bar needs to be – is it better than the average sensible and experienced driver?
Otherwise if you replace all 80% of the good drivers with waymos and the remaining 20% stay behind the wheel, accident rates are going to go up not down.