I think the L4/L5 debate can be greatly helped by people realizing that the majority of human drivers on the road are not L5-capable. A sizeable chunk are L3s and not many are L5s. The way it works is that people simply don't go out in conditions they don't feel comfortable in (snowsquals, etc) and will never attempt areas they think are beyond them (comfortably driving in suburbia, but never attempting to drive in N…
Regarding snow squalls, I don’t think it is a reasonable interpretation of L5 to say that the vehicle must be “smart enough” to do things it physically is incapable of doing. I think the difference between 4 and 5 is that 4 may refuse to operate in scenarios that the vehicle could otherwise safely operate.
Part of human refusal to drive is also a significant advantage to human judgement: if the road is a sheet of ice and the car is sporting all-season tires, even an L5 should refuse to operate.
The bad drivers you talk about are an L4 not an L3. L3s can just stop driving the car at any moment, the human equivalent is like someone suffering a medical emergency while driving.