Arright, I guess I have to do it for you: You are more or less right in that that radiation is a two-way street and the temperature of both the source and sink determine the heat transfer. So the Stefan-Boltzmann equation predicts the heat loss of an object by radiation toward another object of a known temperature and thus also the temperature of the object given a certain constant heat input. If your idea is correct, we could simply put an object into space with a constant heat generated and see what the resulting temperature is. From that we can calculate the temperature of whatever it is exchanging radiation with. If your idea is correct, we can use this experiment to detect the temperature of what the radiation is exchanged with - even if we can't see it, based on the energy exchange. Agree? And if the object is exchanging heat with nothing, it should get very, very hot according to you: which would also indicate the Stefan-Boltzmann equation breaking-down since the Stefan-Boltzmann equation predicts that if you take away the other object by making the heat sink temperature 0, you actually get the best heat transfer, not the worst. Agreed? So we can test your idea against the Stefan-Boltzmann law and see whether your idea is correct or if the Stefan-Boltzmann law is correct about this special/limiting case. Right?