FTR, I bought my 55" LG OLED (OLED55C7P C7) in May 2017. It is on 6 - 8 hours each day. I have noticed no degradation of the display in any way. It still looks
gorgeous especially with a high quality hi-def source like 4K Blue-ray.
I have noticed every couple months it will yell at me, telling me it is going to or has already run a self-maintenance "Pixel Refresher" routine. I don't know if this refresher routine is actually doing any good because I don't really notice any before and after difference. But then that is why you do "routine" maintenance on things - to "keep" them running optimally.
So again, after nearly 5 years, the blues are brilliant and I see no evidence of any burn in or other image quality problems. And I have recently had guests (with younger eyes) come over and ask if that was a new TV because it looked so good.
All I can say now is when this LG OLED finally dies, I will definitely get another LG OLED TV. That's the best endorsement I can offer.