My guess is that they're running training tests on the ON, using USS as validation. The holiday update changed parking visualizations to give us a pseudo birdseye view as we park, but kept the USS distance lines for those cars with the sensors installed. I wouldn't be surprised if the next update or so turns on ON distance numbers in addition to USS distance lines to increase confidence. Once they're close enough, we'll see a roll out of vision parking functions.
In the meantime, the easiest solution is to create a parking profile as a copy of your main driving profile, with Advanced Driver Assist disabled. When you come to a parking lot, switch profiles and park. When you get back into the car, switch profiles back to your main, or use the feature that autoselects your profile based on your bluetooth connection. Three screen taps - not too difficult.
