It depends on the game. If there are a lot of game simulation calculations to do for every frame, then you're going to be CPU constrained. If it's a storybook that you're walking through and every pixel is raytraced using tons of 8000x8000 texture maps, then it's going to be GPU constrained.
Most games are combinations of the two, and so some people are going to be CPU limited and some people are going to be GPU limited. For games I play, I'm often CPU limited; I can set the graphics to low at 1280 x 720, or ultra at 3840 x 2160 and get the same FPS. That's CPU limiting.
I recently swapped out my AMD 3800X with a 5900X as an alternative to a full platform upgrade. I got it mostly for non-gaming workloads, however I do enjoy games.
Paired with my aging but still chugging 2080Ti, the max framerates in games I play did not significantly increase.
However I did get a significant improvement in 99-percentile framerate, and the games feel much smoother. YMMV, but it surprised me a bit.