Looks pretty idential to my MBA M1. Thanks for posting your photos! These are valuable information for all confused with this issue whether they have a faulty unit or if this is a feature.
I'm also leaning to that it must be coating or similar causing it. It cannot be just few faulty units as they seem so idential. If it was some odd fault, there would be some variation how it shows but these are all just too identical for that.
And I agree too that white and bright images are pretty much perfect in uniformity in MBA, even better than my MBP 13" 2019 was even that one had perfect black image uniformity and higher contrast ratio. This is one of the reasons I'm leaning on keeping my MBA. Also I'm considering MBP M1 probably is soon obsolete model likely because there is just so little difference to MBA to justify the price difference.
The only reason I would consider a MacBook Pro over an Air is battery life. If you really need those 2-3 hours more and can’t carry a cable around.
but even then: the air has an easily changeable battery while the pro battery is glued in. Battery service costs almost twice and if you can hold a screw driver you could do it yourself with the air.
The throttling is obsolete because there are already tests with heat pads that you put under the lid to help spread the heat better. Combined with a stand the air didn’t even throttle after 10 minutes...
I don’t care about the Touch Bar. I don’t use neither this nor the f keys to an extend that I could care about that.
the sound is louder in the air.
and as you say, the pro entry model will be obsolete when the 14” comes out. The air will probably keep its value much longer for the very same reason.