In the thread at
https://www.mobileread.com/forums/sh...d.php?t=292336 I posted comparison of my Oasis 2 screen with my Voyage screen at quite a few brightness levels, including 12. I think both my actual screens look better than my photos, and I do not notice the gradient. But I know that quite a few people that post complaints about gradients would find my Oasis 2 screen unacceptable. So there is variation in perception and variation in the actual devices.
As evidence that my photos are not over exposed, the thin, dim, gray horizontal lines are clear and visible across the entire width of the screen, unlike in the photo in post # 5 above.