I would assume that almost no one is running 720p resolution on a 1080 Ti. : P
And if you actually look at the frame rates there, the Ryzen 2700X averages 550 fps at that resolution in CS:GO, while the 8700K averages 836 fps. So sure, the 8700K is 52% faster at 720p in that game, but even the minimums were above what a 144 or 165 Hz gaming screen can display, so it's unlikely those extra frames would make any appreciable difference.
And realistically, most people would be running a 1080 Ti at 1440p resolution or higher, where the only other game to see a big performance difference was Starcraft II, another somewhat older, single-threaded game. And with a less high-end graphics card than that, you would likely see performance differences more like those 1440p numbers at 1080p, or less still, depending on the card. Unless one has a rather high-end graphics card relative to the resolution they are running, along with a high refresh rate screen, the merits of going with a high-end CPU are questionable.
In any case, it sounds like they already bought the hardware, and it is an upgrade over what they had. I would have to agree that waiting a few months to see what the 7nm Ryzen CPUs have offer might have been worthwhile though, at least from a cost perspective.