This is what I don't get. If I have a 1080p why game should run at 4k?
It's the native Res. Why do xbox games run at 900p if we have a 1080p panel? Native res.
Unless the dev puts in extra rendering options ala tomb raider. If you play a game on pro, of course it is gonna run on pro mode. With pro shenanigans.
Edit: Also it is important to make a distinction between native 4k and the sorcery 4k ps4pro does. The latter is more prone to rendering artifacts and blurry IQ. Whether you notice that or not I have no idea. See Quantum Break for X1 for reference.