Well, first of all, we should probably clarify that the original claim was that Bayesian rationality was a systematic way of producing good theories, and therefore presumably was meant to contrast with scattershot or intuitive ways of producing good theories,

That just makes matters worse. Bayes might systematically allow you judge the relative goodness of various theories, once they have been produced,, but it doesn't help at all in producing them. You can't just crank the handle on Bayes and get relativity