I think LTT did a video on this recently actually.

The truth is there are some inflection points, but your chosen gaming resolution is going to affect things the most. If you are playing in 1080p, then you are leaving true performance on the table to not upgrade the rest. But if you are gaming at 4k, the GPU carries 95% of the biggest burden, so you are seeing only 5-10% improvements from changing your whole damn motherboard and cpu.

As time goes on this will change. But especially since 4k high end gaming is so intensive, the gains on cpu aren’t massive. 1440p you get some moderate improvements from cpu / memory, etc, but 1080p is where you can see huge uplift.