The role of the CPU is not to limit the full potential of the GPU. What i said was for a particular monitor specs, and it is true. In the above video, there is a comparison between 2080 and 2080ti. The 2080ti is of course the better card. Instead of pairing the 2700x with 2080ti, if it would have been other way around, then there would have been more difference in the benches than what it shows.
The above two builds will perform the same with the monitor. Note that the monitor is the limiting factor here. For a 1080p/60hz monitor, anything above a 2060 is wasted potential as the monitor is too weak to keep up with the faster cards. As mentioned in my earlier post, if a 9700k can give you 5yrs, the 9900k can give you 7-8yrs easily. It is easier to upgrade a card than upgrading the entire platform later on. And if you have a stronger platform, your base remains solid and gives you that much longevity.