Again, ETTR is about noise reduction.
George
The predominant source of noise in digital imaging is photon shot noise which is inversely proportional to the square root of the number of photons collected by the sensor (regardless of sensor size BTW).
When the dynamic range of your camera exceeds the dynamic range of (elements you care about in) the scene increasing exposure to place the scene at the top end of the camera dynamic range increases the number of collected photons and so reduces noise. The increased exposure needs to be corrected in post.
How much (if any) ETTR is possible depends on camera and scene dynamic ranges. Also remember that ISO setting has no effect on number of photons collected or (the correct definition of) exposure.
As for the OP’s request. If you assume exposure compensation was entirely for ETTR then you are also assuming the camera’s metering was correct. Why would the camera’s assessment be any different or better than one of PL’s automatic exposure compensation settings? The only way it would be significantly different is if in camera you spot metered or changed the scene after metering.