there is no such thing as general "CPU (or whatever else) is bottleneck".
each component does specific tasks for specific applications.
In games CPU does the "world model" calculations, AI like NPC calculations, object interaction calculations, game logic, physics, sound etc.
At some point, CPU should tell the GPU what and where to draw - that's draw calls.
GPU only have to render the frame.
So most in game settings affect GPU performance. But some of them affect CPU as well. for example draw distance or number of characters.
For some games, like CS:GO, where the world model is simple and the game is not multi-threaded, changing CPU does almost nothing.
For other games (which are the most of modern games), you will see a benefit from going to a more threaded CPU like i7-6700K or i7-7700K.
It won't necessary be the higher AVG FPS, but more consistent FPS with much smaller drops - that usually means no stuttering/freezes and less control lags.
you can see semi-decent example of i5 vs i7 here
https://www.gamersnexus.net/guides/2773-intel-i5-2500k-revisit-benchmark-for-2017/page-3
the games where there is no difference for the top 3-4 places is due to the GPU limitation.
pay attention to the 0.1% low.