The parent comment said the bar should be "significant improvement" over the average performance of human drivers.

Then you said, "this isn't reasonable", and the bar shouldn't be "slightly better" or "barely better". It should be at least better than the 75th percentile driver.

It sounds like you either misread the parent comment or you're phrasing your response as disagreement despite proposing roughly the same thing as the parent comment.

All depends on what you read as "significant improvement".

A 20% lower fatal crash rate compared to the average might be a significant improvement-- from a public health standpoint, this is huge if you could reduce traffic deaths by 20%.

But if you don't get the worst drivers to replace their driving with autonomous, that "20% less than average" might actually make things worse. That's my point. The bar has to be pretty dang high to be sure that you will actually make things better.