The two-year old Surface Pro 5 offers essentially the same display experience as the latest Surface Pro 7 down to colors, contrast, brightness, response times, and more.
https://www.notebookcheck.net/New-name-same-hardware-Microsoft-has-been-using-the-exact-same-LG-Philips-panel-for-its-Surface-Pro-series-for-the-past-three-years.442859.0.html
So much panel variation...
If they updated the panel in the 7 people would immediately question why they didn't update to the 13" used in the X... and if they used the same panel that's in the X they would be losing one of the big selling points of the X. It would put them much more in direct comparison... same screen... more power for 7... more battery and less software compatibility for the X.
Unfortunately the yearly update cycle and need for new products in the mix... and the need to maintain backward compatibility with chargers and docks means that the Surface Pro may 'look' cutting edge... but it rarely is.
The biggest cutting edge thing about the Surface 6 and 7 are 4c/8t i5 processers in a fanless tablet chassis.