Not sure I follow. I would think the rating of how much better they are would be applied only to the non-culpable driver? But you are saying the metric should taint that driver with the fact that they didn't manage to avoid an accident caused by someone else? I sort of get it but not sure if it makes sense... can you say more?
Or maybe I'm overthinking it and you're just talking about how hard it is to get the statistics (number of accidents) down overall?
You're overthinking. Fault is a legal construct to help decide liability. What we really care about is if we're dead or not. Insurance is there to take care of the rest.
Since drivers under the influence are less likely to die in an accident because most drugs either relax the muscles or delay reflexes enough to keep the body relaxed during an accident, preventing a lot of potential injury, it's an important nuance to consider. If the people most likely to drive drunk are the least likely to adopt self driving cars, there is an absolute floor to how much safer they can be.
Or maybe I'm overthinking it and you're just talking about how hard it is to get the statistics (number of accidents) down overall?