I found this thread because I got an iPhone 7 and feel like the bottom part of the screen has a bit less brightness, with a slightly more orange tint. I'm not sure if I'd go so far as to call it a problem though, because I feel like the
Display Mate review sheds some light on this. For starters, the more accurate colors give the screen a warmer, more orange tone than the blue-skewed screen on my 6.
But the bigger point is the display angles -- Display Mate finds that there is a larger decrease in brightness at an off-angle than there was for the 6. When I used my phone I tend to look downward at it from the top edge, such that I'm looking at the bottom from a sharper angle, which yields a larger decrease in brightness. Combined with the warmer color tone, this gives the bottom of the screen a darker, more orange hue. If I hold the phone so my eyes are at a 90-degree angle to the bottom 1/4 of the screen, the screen looks more uniform.
I speculate that the pixels were aimed "downward" a bit more than on previous screens to give a more uniform look for people who angle the phone slightly away from their eyes while using it. And many of the pictures on here of uneven screens are taken from a position square to the top of the screen, so I wonder how looking at those square to the bottom would look.
(So yes, what I now realize I'm saying is... maybe you're holding it wrong?

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