Several PC scaling comparisons have already been done on the Youtube circuit...
Max FPS with a 3080 at 1080P is currently extracted from 10900K or 10700K...(The upcoming 5800X might indeed change that!)
The difference is less pronounced at 1440P, and a non-player at 4k..
(The 3900X does not offer much extra performance, gaming-wise, over the 3700X/3800X, IMO)
Yes, there are very few, if any, games that see an increase in performance because you're using anything from the current AMD product stack higher than the 3700x. There just aren't sufficient optimizations to see more than 8 cores with hyperthreading translate into tangible gaming performance gains. Unless of course you are also recording, streaming, encoding, or performing OTHER simultaneous heavy multitasking WHILE you are gaming, in which case THEN those extra cores are probably going to make a difference.
You have to always consider, EVERY SINGLE gaming performance review you see is done under lab conditions and they are NOT going to be doing ANYTHING else while they are doing benchmark comparisons between CPU models. So that consideration can definitely change what CPU model you might consider to be the top choice based on whether anything higher offers additional benefit or not.
Besides which, we do of course know that just because something hits a ceiling today, doesn't mean it will next year, or in six months, or next week, based on newer games with newly optimized code, new or refined APIs and changes to Windows itself. Four years ago, there was almost nothing that could possibly have made any substantial use of an 8 core 16 thread processor on the consumer side of things, and not just in gaming, now, there is a lot that can, but there is not a lot that can beyond that on the same platforms. But it's changing constantly.