The test setups at Techspot for the 9400f / 2600x review are kind of strange.
$220 x470 Gaming X and $120 H115i Water cooling for the 2600x.
$280 Aorus Master and stock cooler for the 9400f.
$109 16GB 3400/CL15 for both.
However, the 9400f is clearly a budget CPU, so I don't think anyone is going to be pairing it with basically $300 mobos. The only reason to go hog wild with a z370/390 selection is for extreme OC with the unlocked CPUs.
The $110 Asus Z370 Prime can easily push the 9400f at higher numbers than they got for their config. Toss a $20 212 clone on it and use Intel XTU to lock @ 4.1x6. The 9400 also doesn't really need crazy ram speeds, your budget $69 AR 3200 kit @ stock XMP will still be better @ 6C all core 4.1 than looking for the more expensive ram.
By going 9400/AsusZ370/212/3200, you get $340, basically a full $200 cheaper than the Techspot build, and faster to boot.
On the 2600x side, to stay at that same $340, it's totally doable with Aorus x470 $109, stock cooler, same 3200 16GB kit. Literally almost half the price of their frankly silly $630 combo with mega Mobo and watercooling.
Between the budget versions of these builds, the 9400f would definitely gain performance, while the budget 2600x would lose very little at about half the cost.
Normally I don't think test configurations are all that relevant, but the choices made there for obstensibly budget choices seemed slightly misleading to me. As with more realistic components for each build, the Intel would be slightly faster, the Ryzen ever so slightly slower with stock cooling and 3200 mem.
Now some people I'm sure do go out and pair a bananas Mobo with a budget processor, but I've personally never seen it, not in 30+ years in the industry.