Sure, you can model humans as controllers that receive some reference and track it, just as you can model a human as a set of "if-then" loops, but so what?

The difference is that humans are not like control systems, they are control systems, and are not and cannot be modelled as sets of "if-then" loops, whatever those are supposed to be.

How would that model do any good compressing our description of how human minds work?

That presumes we already have such a description. PCT provides one. It provides the possibility to obtain actual understanding of the matter. Nothing else has yet done that.

And if people are control systems -- that is, they vary their actions to obtain their intended perceptions -- then that implies that the traditional methods of experimental psychology are invalid. Correlating experimental stimuli and subjects' responses tells you nothing. Here's a psychologist writing on this, the late Philip Runkel.