i wonder how will the phone seller explain this to customer in layman term..and each of the big oem has different aspect ratio on their phone, iphone, s8, g6 etc. etc.
Once you start playing games like excluding the top of the iPhone X display which can only be used for status icons you surely have to be consistent. After all, the equivalent icons are part of the display on other devices. And if we start removing parts of the display area that are not fully functional, how should you account for the curved edges of the S8 display, which are less useful than the flat bit? When you compared iPhone X to S8 areas you removed the "reduced functionality" part of the iPhone display but kept it for the Galaxy, since the diagonal you quoted for the S8 includes bit of the display that's folded down. I'd argue that this either overstates the usable display area of the Samsung or understates the total display area of the iPhone.
Maybe it's better to keep things simple by just comparing to flat-screened devices, which would leave only one oddity you had to decide how to handle rather than two.