In the video, der8auer elaborates to basically claim a completely lack of consistency among the quality of VRMs and their heatsinks in various manufacturers. In his first test, he takes a CPU that is known to do 5.0 GHz and on a Gigabyte Aorus branded mainboard found himself unable to even hit 4.6 GHz with dangerously high VRM temperatures. He goes on to blame the heatsinks on the VRMs, going so far to call the Gigabyte solution more of a "heat insulation" device than a cooler, as a simple small fan over the bare VRM array did many magnitudes better than a simple standard install with the stock VRM cooler attached. After an MSI-branded board did similar, it became clear this was not an isolated issue.
der8auer splits the blame among Intel and the motherboard makers. Part of the reason is that Intel pulled the launch from August to June, which gave motherboard makers very little time to optimize their products.
He also complains about an 8-pin EPS cable hitting a temperature of 65°C because many motherboards have only a single 8-pin connector, but TechPowerUp consulted with Jon Gerow (Jonnyguru) and reports this could be because of the PSU he used.