> In practice, much of the article seems to be about the problems introduced by rigid typing … But that's a non-issue in the FP languages mentioned above since they tend towards the use of unstructured data

Haskell doesn’t have this problem. None of the “rigid typing” languages have this problem.

You are in complete control of how strictly or how leniently you parse values. If you want to derive a parser for a domain-specific type, you can. If you want to write one, you can. If you want to parse values into more generic types, you can.

This is one of those fundamental misunderstandings that too many programmers have, and it seems like it’ll never die.