A hollow heatpipe has better thermal transference than a solid heatpipe, simply based on physical limitations, a hollow heatpipe having much greater surface area when you consider the inside and outside surface. Heat travels best at the surface. However, air and most gasses act more as an insulator than a conductor for heat, most liquids being better conductors. It's the basis of why most all 'aircoolers' use liquid filled heatpipes, better and faster thermal transfers up the entire length of the pipe (the liquid holds the heat longer, also, so the top of the pipe sees more transfer action to the fins). Solid metals dissipate heat very quickly, but also absorb heat quickly, without the liquid center, the heat would stay relatively close to the base of the cooler, which would act as an insulator to greater heat dissipation. By using a liquid core, more heat is pulled away from the cpu surface and spread out along the entire length of the heatpipes. Hmm sounds exactly like a vapor chamber..
With aios, the cpu heats up microfins at the underside of the pump. The diaphragm pushes the liquid through those fins, which then dissipate heat energy to the liquid, before being shunted down the tube to the radiator, which dissipates that energy before returning back to the diaphragm. A full custom loop is exactly the same except the pump diaphragm is not built into the microfins chamber on top of the cpu. The glaring difference between that process and a vapor chamber or even heatpipe is that it's a totally mechanical process, whereas vapor chambers work on a chemical process using innate chemical properties of the liquids energy absorption and state to provide motion.
The only similarity between vapor chambers/heatpipes and aio/liquid cooling is that they all use liquid in some capacity. But there's a huge difference between a chemical process and a mechanical process, which is the underlying difference between an aio and a vapor chamber cooler.
So sorry to contradict aisalem, but you got it backwards.