I can attest to the OLED burn-in. My three-year-old Samsung Note 4 has a very noticeable bar across the top, from the dark status line above what is usually a light background on everything else. I guess the rest of the screen is what is burnt in and the status bar area is closer to its original state.

I don't notice it most of the time, but it really stands out on anything full screen. I think I would be rather annoyed if a three-year-old laptop did this.