It's very difficult to find games that are bottlenecked by graphics cards nowadays (at 1440p60 or below). There are three major reasons why this is happening:
- Nvidia has been killing it in graphics card design relative to the competition. Consider that a GTX 1070, released 30 months ago, can go all the way to 1440p60 comfortably.
- Nearly every game has to be playable on consoles, and consoles are all running AMD's last generation chipset.
- 4K is still the "storm on the horizon" that no one's graphics cards are truly ready for in an affordable way.
All of that combined really means that raw graphics quality in games hasn't improved a lot in the past four years.
So, most games will continue to show increased performance the more clock you throw at a processor. Combine that with more and more games optimizing for more cores given the prevalence of 6-8 cores chips on the console market and in gaming PCs, and this should make sense to anyone.
It should be said: This is why cloud gaming is quickly becoming a real thing. Beyond connection speed, graphics cards were always a huge bottleneck in making that cost affordable to cloud providers. Today, the graphics card isn't a bottleneck, and all the cloud providers have an abundance of them in their data centers for AI-focused work. And if neither the cards nor the connection speed could handle 4K anyway...