To be fair, it's standard with any OLED screen. The iPhone X is no different in that regard from a Samsung or Pixel device. (In fact the Pixel uses LG displays and is much worse from what I've heard.)
So now, rather than "hahaha Pixel 2 owners - SUCK IT!" it's the far less satisfying "hahaha Pixel 2 owners - our displays burn in somewhat less than yours !"?