A phone being returned doesn't have to have anything to do with if it's good or not. I've seen people return devices because they didn't like the color, or because a new promo came out and they wanted to be eligible for it.
I've looked at various examples of the S8, Note8, iPhone X, and Pixel 2 XL. All of them have some degree or another of color shift, and in some cases, the Pixel wasn't the worst offender.
I'm struggling to understand your reasoning about the Samsung vs LG displays. You're saying LG is on generation 4 and Samsung is on generation 10, and it's unacceptable. The reason LG isn't at the same generation as Samsung is because they got out of OLED panels in smartphones a few years back, opting for LCD instead. Now you may ask why Apple doesn't have that issue, and that's because they're using a Samsung panel. They didn't develop their own technology, they bought it off someone who's already done the work. The only way LG could skip generations would be to either steal the tech from Samsung, or one of their engineers. And more than likely, those engineers would have a non-compete in place barring them from working with a competitor or divulging and trade secrets they were privy to in the employ of Samsung.
You act like it's no big deal for these companies to send out another device hoping it might be better. Most any company isn't going to send out a replacement product if there isn't an almost a guarantee that it will fix the problem. And in many cases, the first thing they'll ask is, does the issue prevent the device from operating.
If it where happening all the time at any angle, then I could see it. But if you have to change the angle to one you're not going to use it at in the first place... You know what, buy a different phone and be done with it.