Caporegime
I'm not even going to watch the video because it's obvious clickbait, but...
... while CPU overhead would seem to be the obvioius culprit from looking at simple benchmarks, there's more to it than that. Chips and Cheese did an excellent analysis of the actual work done on a 7900XTX and 4090 to render each frame, showing that there are architectural differences that explain the unusual performance delta - for instance the 4090 doesn't have enough registers.
Interesting read thanks, i may have to read it twice tho...