That's not how Tesla has defined it every time it's talked about "shadow driving".
See these:
Tesla’s new Autopilot will run in ‘shadow mode’ to prove that it’s safer than human driving
Tesla starts pushing new ‘Enhanced Autopilot’ to entire fleet in shadow mode only
Tesla adds ‘calibration period’ for vehicles with new ‘Autopilot 2.5 hardware’
In that last one, we have a Tesla spokesperson describing shadow mode specifically: "During that process, Automatic Emergency Braking will temporarily be inactive and will instead be in shadow mode, which means it will register how the feature would perform if it were activated, without taking any action"
"Shadow mode", at least as it applies to Tesla, is exactly what you're saying you want in terms of real-world data.
I get the legalize. Which is how Tesla believes they get legal protection while wanting and nudging their drivers to let go of the wheel. Are there no videos where Elon let's go of the wheel? Are there no modes where you can or are supposed to be able to let go of the wheel? Please if Tesla really wanted that L2+/L3 to not happen the AP would never allow it for more than a second.