Comment by Nevermark

Agree with your characterization.

The conversation was about harnessing energy, from heat, in orbit.

Heat pumps take energy to move energy. But you can't power the heat pump from the heat it is already pushing against the heat gradient.

Waste heat can be used, if there is a difference in heat to work across, but not if there isn't. A datacenter in Antarctica could recover energy from waste heat, against the freezing outdoor temperatures.

In orbital systems, the problem is getting rid of heat, so there isn't some cold place to use to create a heat gradient and harvest energy. Space is cold, but particles are so diffuse they have little heat energy capacity, so essentially a heat insulator, and not useful to create a gradient. Thus the use of radiators.