The disaster of terrible AI, aborted A-Life, random spawn spam and NAFO agendas aside S.T.A.L.K.E.R. 2 is a pretty good showcase of diminishing returns in terms of graphics, games being made today don't look a whole lot better than games made a decade ago, throwing in PBR and very poor approximations of ray-tracing, something they had done for very cheap with passable methods of faking it for a long time, doesn't do as much as you might think for the game. The biggest difference is foliage density.
This video is a really good comparison and is well-chosen for the point you're making, for a lot of reasons. For one thing, look at how much personality Sidorovich lost when he was uprezzed. I have found this to be the case across the board with 3D games from the past decade compared to the great ones of the past: in the old days, human characters were always
designed by artists, and therefore the characters felt like works of art, and had the kind of personality which is only present in works that have a genuine human touch. Like look at original Sid there; he is a really weird guy. You have to imagine that he would be, to hold down in his position as a wealthy trader surrounded by a bunch of heavily armed and hungry young men, most of whom are borderline-criminals. Sid is like the archetypal "Fat Man" underworld boss in so many old noir films. And so he looks like kind of a freak. He has big bug eyes and an imposing countenance, and seems like a guy you wouldn't want to mess with. But when you look the "Sid" in Stalker 2, you just see "a guy." It's so lame. It's just some actor whose face was digitized, almost certainly--and even if it isn't, it completely lacks the oddity and personality the original Sidorovich has, because character and imagination and strange creativity have been sacrificed upon the altar of "realism."
I was playing Call of Chernobyl a while back and I played some Autumn Aurora directly after, and I had this same impression even with that comparison. Like the Stalkers you run into in AA, the original SHoC ones, are really freaky-looking guys, skinny and with strange, twisted faces. They look like something out of a dream or a cartoon, and their strange appearance really adds something to your impression of the Zone. Even in Call of Pripyat's assets the creep of "realism" had already started to erode some of the character and personality of the original vision, and the game's world feels notably "dry" and less atmospheric compared to Shadow of Chernobyl, and especially compared to Autumn Aurora, which is a masterpiece mod created by one guy who is clearly a genius. Great atmosphere comes from hours and hours of personal investment like that, not from "adding a bunch of grass in UE5."
You're right about the diminishing returns of graphical improvement too, and the over-reliance on foliage. Stalker 2 has way too much of it. Like look at the comparison with the original Novice Village there with its clean, dry road, which makes sense for a frequently-trafficked area, vs Stalker 2's boggy swamp in the middle of the same area, full of puddles and overgrown with plants. It's pretty unlikely that area would actually be like that, and it just looks stupid and overdone to me. "Look at all the things! Look, water!" Also note at 5:30 the NPC who teleports and then starts doing a running-in-place animation. The animations in this game are also a major downgrade, and every clip I've seen of towns has guys walking around aimlessly in bizarre, fake-looking ways which weren't present in any of the original games. It looks like it's just a bunch of junk animations wholesale imported from some UE5 animation library and incorporated without fine-tuning any of it to make sense, vs the animation in the original games, which was done much more by hand, and therefore feels very natural and real. It's the touch of the individual artist's hand that makes any kind of art any good, and Stalker 2 feels like it has very little of that.