Completely agree with this. It will be ridiculously difficult to get to Level 5 automation in cars. It's decades away, not years. Ironically though, part of the reason it's so difficult is that during the transition the roads will still be populated with human-driven cars. If we passed laws to the effect that "as of date X, no human-driven vehicles or pedestrians will be allowed on roads in the set {Y}", we could get…
One could make the convincing argument that Waymo's vehicles are already at Level 5; where they probably struggle (I have no examples or data on this) is probably in inclement conditions (rain, snow, fog, etc). That said, even in such conditions, they probably perform much better than a human driver.
For instance, most human drivers in such conditions - even when they struggle to see the road clearly - continue to drive anyhow, mostly blind, instead of doing the right thing and pulling off to the side of the road and waiting, which I bet is a behavior that Waymo's vehicle performs when it struggles beyond a certain level.
In other words, Waymo's vehicle is likely better at determining when NOT to drive, and acting on that determination, instead of being stubborn and irrational in the face of evidence to the contrary.