If the CPU can put out 100 FPS in a given game but with the in game settings or resolution the video card can only put out 60 FPS then it has limited the CPU.
A bottleneck is when one part cannot literally perform its function because another part of the chain is too busy to tell it what to do. Tell me, does a GPU tell the CPU what to do?
In any case, the CPU's role in running a video game is to complete all of the logic (like input handling, game logic processing, AI, etc) such that in-game time lines up with real time. Presenting that information, be it audibly or visually, is only a benefit to the human and not strictly necessary for the game to work. If you want to say this is dumb, I would point you to say how Source engine games work: they create a server (which includes single player, it's just that the server has a max player setting of 1 and you can't change this while the server is running) that the players connect to. The game runs just fine without anyone in it, which means it runs without needing to process audio or video.
The only way for the GPU to bottleneck the CPU in this regard is if the CPU literally waits for the GPU to render a frame. But this isn't how modern game engines work because then frame rate would dictate how fast or slow the game runs.