the numbers you extract will be badly inaccurate most of the time

As its the case with an myopic view on any Bayesian inference process that involves a lot of noise. The question is just whether rationality is about removing the noise, or whether it is about something else; whether "rationality is more than ‘Bayesian updating’". I do not think we can answer this question very satisfyingly yet.

I tend to think what Cumming says is akin to saying something like: "Optimal evolution is not about adapting according to Bayes rule, because look at just how complicated gene expression is! See, evolution works by stories encoded in G, A, C and T, and most of them get passed on even though they do not immediately help the individual!"