a 4C 8T like the 7700k paired with something like a 2080ti (or 3060 ti assuming it actually exists) will have at most 10 fps lower than newer CPUs, and that's in 1080p. The more GPU bound you make it, the less difference the CPU makes as long as it's fairly modern. There are special cases such as RDR2 where you can see something like this:
But overall, CPUs are starting to make less and less difference when it comes to gaming.
There is no doubt that cores and threads make a huge difference in other tasks, but in games it's incredible how much you can cheap out on the CPU nowadays.
It would indeed be interesting to see how this changes in the future, but at the same time, 6C is becoming as affordable as 4C used to be, so if the C/T minimum starts moving up, it won't be much of a problem for gamers who want to run the latest games.
Just look at it, i5 9400f is a 6C (yes it has only 6T, but it still brings insane performance). The point here is not that the i5 9400f is a beast CPU, no, the point is that in my country you can get this CPU for 100 euro already. The fact that people on a budget can get this CPU for 100 euros is just a blessing. I remember paying 200 euro for the i5 6500, how things have changed..