1. Waymo is autonomous 100% of the time. It is not possible for a human to actually drive the car: even if you dial in support, all they can do is pick from various routes suggested by the car.
2. No, I'd guesstimate 90%+ of Waymo's mileage is city driving. Waymo in SF operates exclusively on city streets, it doesn't use the highways at all. In Phoenix, they do operate on freeways, but this only started in 2024.
3. Phoenix is driving in easy mode, but San Francisco is emphatically not. Weatherwise there are worse places, but SF drivers need to contend with fog and rain, hilly streets, street parking, a messy grid with diagonal and one-way streets, lots of mentally ill and/or drugged up people doing completely unpredictable shit in the streets, etc.