I just tested with this image and it does distort the white on black text at the top screen only. I didn't notice a difference on the black on white text. So the issue is real and can be seen in this specific test, but I don't think its something that should sway people from buying this display. Even if both the FV43U and 43QN90B have the same issue, and given the difference in price, I'd still choose the samsung for better dimming, remote, and smart tv features. There aren't that many options at this size and I think this is probably the best unless you are comfortable with an oled.What test pattern? It absolutely has to be unscaled, whatever image you have used.
This is the old image I made to test for the problem on the FV43U (had to go hunting for it heh). In theory all the grey lines and text should be the same colour. If your screen has the issue, the horizontal lines on the grid get directly affected by the white or black pixels that sit above them, causing them to look lighter on the white canvas and darker on the black one. Again, this must be viewed with no scaling, desktop or browser, with the TV at its native 4k or it will smoothen the image and ruin the test.
View attachment 496914
Yes, the text is tiny. No it isn't a real world example of text you'd read on such a display. This is simply to test whether the pixel interference is a thing on your panel.
Also view this image at both the top and bottom of your screen - as per the Amazon review posted above, it is entirely correct that the issue is at its worst at the top of the screen and virtually non-existent (but still there if you know what to look for) at the bottom.
Some people can happily live with this dent in image quality that can't be fixed, I never could.