I just got the Pixel 7 Pro and am comparing it to my OnePlus 9 Pro.
I bought a LUX meter and opened a 50% white pattern.
Looks like this:
I configured both phones for manual brightness.
I choose "natural" for the color setting since the Pixel didn't have the "vivid" I usually use on the 9 Pro.
The Pixel 7 Pro registered 800 LUX while the 9 Pro absolutely demolished it with 1800 LUX.
There's no comparison. My 9 Pro running an AOSP ROM absolutely destroys the 7 Pro for maximum manual brightness.
I'll test auto-brightness later today.
Edit: See post #44 for updates