Fair point, that might work if: 1. a public safety/citizens oversight committee does its job consistently, 2. isn't loaded with police-friendly stooges 3. and isn't gradually de-fanged over time in terms of its power.
All three things, with time, can be manipulated by any given city hall, which is often lock-step with the police force.
"...but theories need to be tested one way or another and it would provide some evidence"
Agreed. And I say let's look at how they've deployed facial recognition in China to put those theories to bed.