I feel you. I’d probably return it too if I was in the same boat, especially since the issue developed after the restore.
I’m wondering if there was a screen calibration that got wiped by the DFU restore. It would be interesting to see a picture of your iPad next to another freshly unboxed one to see if there is a variation in the backlight.
Yeah i wish i could do that, but then compared to my wife’s 2018 this thing looks amazing. Colours and detail is so much more better. Here is a compare of ours when it was going the 14.6 update.
Honestly I think I’m just being picky and I have a feeling Apple are going to be able to tweak something and make this problem a lot less of an issue. iPadOS 14.7b2 don’t make any difference but I’m hoping iPadOS 15b1 does!