I wonder if the author's issue is due to the author using a Mac. Back when I was at Google working on VR images, my work machine was a Macbook and my home machine was a normal Windows desktop. I realized that images looked worse on my laptop's screen because the native resolution of the display hardware was something like 4000 (numbers made up because I don't remember the specs) but the display was set to 3000. So OSX would incorrectly rescale the image using the wrong gamma curves. Since I was trying to calibrate VR headsets, I spent way too much time looking at gamma test images like https://www.epaperpress.com/monitorcal/gamma.html where a high res pure black + pure white grid is shown next to a set of grays. That was how I realized that my Mac was incorrectly resizing the graphics without being properly gamma aware. I also realized that if I set the OS resolution to 2000, it would use nearest neighbor instead of bilinear filtering and the gamma issue would go away. My Windows desktop had the OS running at the native resolution of the display so this wasn't an issue there. This also wasn't an issue if I had an external monitor hooked up to the Mac and set to its native resolution.
Apple users tend to say "it just works" which is true 90% of the time. But there are cases like this where it doesn't "just work" and there was no easy way to force the OS to run at its native resolution on that specific laptop.
Edit: I tested with the second set of images (the upper body shot) and the problems with the gradient are visible there. But I still can't see a different when quickly flipping through the first part of images on my properly calibrated native-resolution monitor. I _can_ see some banding on one of my monitors that was intentionally miscalibrated so that I could read text better.