Spending more on the GPU is a misconception that needs to be addressed eventually. Game engines demand more and more out of the CPU with each generation, and CPU frame times can only be mitigated by spending more money. There are no CPU related settings to tweak in any game, and if you want to hit 100 FPS mins in multiplayer - which I would argue is essential - then you need to invest in the right CPU.
Also, 'GPU limited' is a tricky term. It takes the best cards to hit 100 FPS minimum at 1080p/1440p ultra. But at least there, you can tweak GPU settings to lower the frame times.
First, spending more on the GPU (in the current pricing situation) is not a misconception, but almost inevitable if you care about gaming. At $250 you get a decent mid-range CPU while the best-of-the-best 9900K tops at ~$500. A $250 GPU is midrange (RX 590, 1060) and there are *four* tiers above that (2060, 2070, 2080, 2080 Ti). Which of the following pairings would make more sense in your opinion? A 2600X with an RTX 2070 (roughly $700) or a 9900K plus a RX590 (slightly more than $700)?
Second, the numbers easily back this up. To use Assassin's Creed as an example, in TR's test the 2600X scores 80 fps driving a 2080 Ti at 1080p (a ridiculous combination of GPU/resolution) and the 9900K scores 91 fps average. In Deus Ex, which is a lighter game, the difference is much greater: 118 fps vs 167. But, if your CPU drives 118 fps do you really need more? Same with GTA V: 114 vs 153 fps. Now, do you want to compare a $250 GPU vs a $500 GPU at 1080p, say the RX590 vs the 2070? And you can scale this even further, comparing the 590/1060 with the 2080, if your budget allows.
I agree that multiplayer may further increase demands for the CPU. I also agree that it's impossible to tune CPU load in the game settings. I also feel that you should plan for a decent CPU (never was a fan of 2c/4t gaming setups, for example). And yes, this may vary from game to game. But overall, I stand by my suggestion to budget more for the GPU than the CPU. Especially in the current pricing situation.