Unless proven otherwise, you would have to assume the DDR4 2666 and 3200 are run at identical timings. Yes it would have been good to know the exact timings, why don't you post a comment on their YouTube channel and see if you get an answer?What is the cas settings for 2666? Its c16 for 3200.
My point beeing if its same cas its kind of misleading test. You can eg run the 8400 on a non oc z board on 2666 c14 easily. You can tweak latency and settings not bandwith.
Steve knows that and to be fair it irritates me he just dint flat out write the latency for the 2666 ram but gives a non link to prior cpu reviews. It comes off a bit fishy.
In more general view many games is latency dependant and thats why we see ryzen perform worse. Especially with slow c16 settings. I simply dont agree in comparing platforms like that. Ryzen needs low latency and a 8700k a good cooler so it dont throttle. If you dont give them that its imo biased testing.
In this the purpose seems to be look 3200 is much better for a 8400 go get you 370 but imo it comes of as more as a sales piece. I need some c14 2666 to confirm.
I am pretty sure the results is more or less excactly the same.
Accusing Steve of foul play and trying to promote Z370 sales is going a bit far, he is one of the best Youtube reviewers IMO and always seems fair in his appraisal of products. Innocent until proven guilty here, I'm going to give Steve the benefit of the doubt based on his track record.
By the way, Techspot tested the i3 8100 and compared performance between DDR4-2400 and DDR4-3200, and shows similar results to Steve: https://www.techspot.com/review/1499-intel-core-i3-8100-i3-8350K/page3.html
Some games just scale well with increased memory bandwith, it's not just as simple as saying if you run at CL14 regardless of your RAM speed you are good to go. I'm sure there are appreciable differences between DDR4-3200 CL14 and DDR4 2400/2666 CL14 in certain workloads and games.