it depends a lot on the type of game and what you care about for that type of game.
if you're playing a AAA singleplayer game, the GPU will almost certainly be the bottleneck. any i5/i7 tier CPU from the last eight years will be powerful enough not to starve the GPU most of the time. when I play this sort of game, I mostly just care about the average framerate. I don't care too much if every 10-15 minutes a complex scene causes a brief stutter. if this is the only kind of game I played, I would just get a cheap midrange processor (unless I had requirements due to unrelated workloads).
on the other hand, when I play a fast-paced multiplayer game (especially fps), I care a lot more about worst case framerates than average. in a game like counterstrike, framerate drops tend to happen when there are smokes, flashes, and/or multiple players onscreen simultaneously. in other words, they happen in the most important moments of the game! while I'm happy to average around 45-60 fps in the witcher, I want the minimum in csgo to be no less than 120. if you have a goal like this, even an old source engine game becomes pretty demanding.
there are also games like factorio where the simulation itself is difficult or impossible to split into multiple threads. singlethreaded performance and memory bandwidth set an upper bound to how big your base can be while still having a playable game.