“The S is a weaker system, but it should have no issue running a current title at 1080p.”
And you know this how exactly? Do you somehow know how large the game is or how much details were put into the game? Have you worked on the game yourself?
Resolution isn’t a standard and will never be, it fully depends on the game and how much graphics hungry it is. You’ll always be seeing lower resolutions in games no matter what generation we’ll be in, simply because as game development becomes more complex over time, and new technologies are applied to games, you’re bound to see hardware limitations come into consideration in a way or another. Especially with power-consuming technologies such as ray-tracing being the current trend in future games, this makes it even more difficult to aim for higher resolution with higher fps.
Best example is right there in front of you, Series X isn’t running the game at 4k/60 despite all the claims of how powerful the console is and it running 4k/60 in all games.