I know this has probably been said already but I think what you're saying is technically false. Let me explain why.
The amount of content that fits on a display (at least for iOS development) isn't determined by raw pixel count, it's determined by 'points' on the display and by scaling. The iPhone X's display has the exact same number of 'points' horizontally as the iPhone 8 despite their different resolutions. Sure, there's about 20% more 'points' vertically in iPhone X when compared to the 8 but they both have the same display scaling. What that means is if you load MacRumors on the 8 and X, the images, text and whatever will all appear the same size on both devices (albeit, you'll just get to see a few more lines of text vertically on the X). If we add the 8 Plus into the mix, things change up a bit because the 8 Plus has more 'points' to work with on the display, in other words it appears to be a denser display.
I suppose a decent way of seeing this in action is if you play with the display scaling settings on your retina Mac. If you set the scaling to 'Larger Text' on a 15 inch MacBook Pro and then set the scaling of a 13 inch MacBook Pro to be 'More Space', which display looks bigger? Or rather, which display can fit more content? The 13 inch one because it has a dense scaling applied. I think that's the same thing going on here with the X, yes it's a bigger measured display and yes it has more raw pixels than a Plus device but the software is more a regular non-Plus device.
It's been said before but I'll say it again: the X is going to feel like a taller iPhone 8, kinda like going from the 4s to the 5. If you're coming from a Plus device, I reckon some people are going to *feel* as though the display is smaller, simply because all the assets on the X are scaled up to be bigger than that of the Plus (at least when web browsing). I'm okay with that for now but I'm certainly going to buy the Plus version of the X next year if they have it.
Sorry if this was a naff explanation, I'm tired and I just want my X