Honestly it's been that way for awhile. There's just way too many varied opinions and experiences, especially for PC. But Steam's refund policy makes it all worth while if you're extremely curious and can hardly wait.
I mean, maybe they're being honest and it's just their opinion? I don't think anyone said the performance has been flawless, at least from what I've seen. I've seen people comparing this to Cyberpunk, and I was able to beat Cyberpunk on PC on launch week without any serious issues. I personally feel like Cyberpunk was a lot worse in some regard, though in my experience it was still enjoyable and doable. I say that because there were genuine gameplay bugs that affected the experience like the whole police system and some other stuff. But I haven't seen anything like that in Stalker 2 yet...
3 hours into Stalker 2 I've seen discolored textures, some random small object getting stuck to my body, ragdolls/items randomly get launched or fly, some weird (and very minor) sound bugs, but that's really it. Nothing that's really breaking my experience.