High level games are far from stagnating, when viewed from usable performance.
Many new games cannot run max settings, 4k, 120hz on any modern gpus. We probably need to hit 8k before we max out on the returns higher resolution can provide. Not to mention most game devs are targeting an install base of $500 6 year old consumer hardware, in a world where the 5090 exists.
That's what I mean by stagnating... most players already can't run with max settings, or even close to them. From the developers' point of view there's not much point raising the bar any higher right now, while the best GPU hardware is so far out of reach of your average PC gamer.