Your autonomy scale is pretty arbitrary and encodes assumptions about the underlying technology and environments the vehicle is supposed to implement and operate in.

The SAE autonomy scale is about dividing responsibility between the driver and the assistance system. The lowest revel represents full responsibility on the driver and the highest level represents full responsibility on the system.

If there is a geofenced transportation system like the Vegas loop and the cars can drive without a human driver, then that is a level 5 system. By the way, geofencing is not an "SAE level 5" requirement. Geofencing is a tool to make it easier to reach requirements by reducing the scope of what full autonomy represents.