OK. And I would say the productivity gains of Haskell are most transparently obvious in the case of the sort of highly complex, stateful, I/O-interacting code you're likely to be writing for a successful tech company.

This doesn’t match my personal experience (having worked on a Haskell web app professionally for a couple of years). GHC does have some cool features like STM, but typical stateful code tends not to be radially more concise or easier to write in Haskell than in other high level languages (compared to, say, code for traversing a binary tree, or implementing a parser combinator library). Others may have different experiences.