I mean to say that a heat pipe not only contains less water per unit area for the phase changing cycle, since its under vacuum, but also the cycle only works at a particular heat per unit volume and temperature range. If you go past the temp range you get runaway.

Water in an active cycle has an almost unlimited ability to relocate heat. You still need to give that heat to something else, but you can pass a kilo of water thru a tiny labyrinth of fins at the heat source and a large surface area radiator with fan on the heat sink side. Vs a few ounces of water trapped inside a pipe running as a heat engine basically. Active pumping is brute force. At some point you won't be able to contain the water pressure if your source is too hot, but there are many different working fluids.

Its irritating when we try designing a new cooling system at work and some guy will always want a heat pipe when clearly there is only a narrow band where those things are effective. Specially annoying if you don't have control over the heat source. If you did have control over the source, then maybe you can tune it for a heat pipe. Car engines don't have heat pipes. Solar collectors don't use heat pipes either for the most part. Heat pipes need a constant source of heat that always stays below their max bandwidth.