[notahacker]

The basic form of the rational actor model assumes nothing more than that the prediction errors an actor makes should be assumed to be unsystematic [unless proven otherwise] for the purpose of modelling. (And by extension, that some empirically observed group-level systematic deviations from theoretically optimal behaviour might be better explained by constraints on ability to act than on inability to anticipate)

Which is a pretty good null hypothesis, actually.

That's entirely consistent with people frequently optimising for ease of decision making, it's just not consistent with slavish adherence to a particular specified decision making function an economist has designed policy around exploiting. The canonical example in macroeconomics being that if a government announced its intention to increase inflation, it would be unreasonable to assume that people weren't rational enough to consider asking for a pay rise.

Epicycles were abandoned because we had a more parsimonious default model, not because we wanted to have a more complex idea of reality and handwaved about maybe being more multidisciplinary.