It's not about the number of edge cases, it's about the overall result. Airbags reduce variance in outcome. They hit a lot of people who would otherwise be unharmed in the fact with a small explosion in order to save a few lives in serious accidents.

The worst case is better and the average case is better because you've eliminated some outliers. However,the median is far worse. The group is effectively being punished to reduce the effect of the worst performing members.

An AI that drives into a partial lane obstruction is only better than no AI for a very small number of cases.