He's talking about thermal interface materials such as those made by Arctic. If you took the time to check the Arctic web site, they state the same thing. In fact, they state that thinner applications of thermal interface material result in better temps. That's why no one wants to gob on thermal interface paste to their CPU expecting that it will work better - because it won't.Eh? This isn't how thermodynamics works. A CPU encased in a theoretical infinite-sized block of copper would be cooled far better than any possible combination of air-cooled heatsinks.
If you consider water-cooling, it may not be true, as water's thermal conductivity is around 0.6 W/m.k, versus air's 0.025. Copper is still several hundred times higher, but given a high enough temperature differential, water's convective aspect could exceed copper's pure conduction.
While what you state about a block of copper is definitely true, in this case, however, your statement is more of a straw man rather than a decent argument.
I'm rather surprised just how many of the "expert enthusiasts" on this site seem to not understand thermal considerations.
What you state is true to a point, but if the maximum opertating temperature of the component's silicon is exceeded, you will end up with a dead chip - end of story. Its misleading, IMO, to state that the junction temperature does not matter and the only thing that matters is pulling away the "power" put into the junction. True, you have to pull away that power, but why you have to do that is so that maximum junction temperature of the device is not exceeded. If the maximum junction temperature is exceeded, the device will fail because its junction temperature exceeded the maximum operating temperature.It doesn't matter that the temperature is, what matters is the heat dissipated (which equals power consumption). If this doesn't make sense, consider gaming on your phone. If you checked you'd find the SoC temp often hits ~90-95C when gaming, yet you don't worry about the phone heating up the house as its only consuming 3-5W of heat at max load. It is the 3-5W of heat that matters, not the die temperature.
If you are worried about overheating VRMs and the like, an air cooler is often better than an AIO because most AIO result in no air flow over the VRMs. If you are worried about heat in general, just do what the review testing did, either select Eco mode, or set your own custom power limit or temp limit.