The X is basically the Plus size, a little smaller.5.8” vs 5.5” is measured on the diagonal.
But they have very different aspect ratios (X is more tall and narrow).
How is this relevant? Normal media, let’s say YouTube videos, are in the same aspect ratio as 5.8” iPhone. On all iPhones except the iPhone X, you don’t get a black border on the sides. But since iPhone X is so narrow, you get a huge border on the sides. The narrow-ness therefore limits the iPhone X when watching media. Basically, the video will have the same size as on a 4.7” iPhone (the non-Plus models).
TLDR: iPhone X is very narrow. Great when holding the phone vertically, absolutely not great when holding the phone horizontally.
I can trade that for having a smaller and "one hand" friendly device.