We're not far away from the release of the Xbox One X. And if you want to get an idea of how that extra power might be deployed in games, compared to what the PS4 Pro can do, here's Shadow of War with a handy example.
According to Digital Foundry, the maximum resolution you can get via the "favour quality" setting in Middle-earth: Shadow of War on the Xbox One X is a fixed 3520x1980. If you want true 4K, you can change the setting to "favour resolution" and disable the dynamic resolution, which will lock the Xbox One X to playing in 4K.
That's more than what the PS4 Pro holds at for the most part. Right now, the game plays at a native res of 1620p, although there's some glaring differences in texture quality when Talion stands alongside, say, a wall.
It's worth noting that the resolution/quality options were present in the PS4 Pro version of Shadow of War. But what's already telling is the advantage the extra memory gives the Xbox One X.
As more users adopt 4K TVs, more and more games will be cramming higher quality textures into the console builds of their games. And as they do that, the difference between the PS4 Pro and the Xbox One X is only going to get more stark.