I've been actually getting the same conclusions - it must be software, not hardware that's broken. I don't believe every single modern laptop has bad screen - there must be some variation in quality, ie. there would exist LED / IPS screens that are ok, but so far I haven't found one on 2017/2018 notebook. With other components you can find devices with great keyboards, touchpads, and I bet the screens that have vivid colors, great contrast, etc. are good on their own, but the source material they are fed with makes them behave bad. Of course there might be screens that do dither on their own, etc., but I don' think that it's done on every device unless it's a technology limitation.
Funny thing is - the screen on my Macbook Pro that used to be unbearable doesn't seem to cause the same issues to me now, it's near 100% fine although I can see it's flaws, they just don't affect me anymore. However I get minor (mild harshness) or major (head pressure, nausea) with every other LED/IPS screen I check for 5-10 minutes.
This whole topic is a complete maze, and I wouldn't be surprised if one day it will get solved all of a sudden when one of OS/graphic drivers manufacturers makes a silent change in their code without informing anyone.