I think you may have misinterpreted his point, which was to compare a 1800x with down clocked memory (2133) to a 1700 with 3200 memory. Overall he is trying to say that going with a 1700 and faster memory is smarter than an 1800x, since they overclock to similar levels anyway.
There are tons of articles and vids on the topic out there, here are a just a few examples looking more directly at memory speeds with Ryzen and gaming, and impacts of CPU overclocking:
They tested across 17 games, and found that going from 2133 CL14 to 3200 CL14 netted a 5.5% gain at 1080p, a 3.3% gain at 1440p, and a 0.8% gain at 4k.
Here the differences are set out a bit nicer between gains from CPU Frequency and gains from memory frequency in gaming
These guys are hard core and this article and video is good because they look at impact on gaming with 3466 memory frequency.
The bottom line seems to be CPU frequency accounts for the largest gains overall, with memory frequency following up, and timings have a positive impact, but third place. The big picture is that by combining CPU and memory overclocking, you can achieve really significant gains at lower resolutions (not GPU bound scenarios). Maybe 25%-35% in some cases.