I work on a Haskell codebase that is close to or over a million lines of code. It’s a bear to work with for a number of reasons but inflexibility to changes in business logic isn’t one of them. People need to stop waving their hands and running around claiming that the sky is falling.

Try writing some Haskell for a while.

Explore the compiler output. If you can ignore the language runtime it’s pretty reasonable. Good, even. There are a lot of cases where GHC can optimize away a lot of things you might think are unreasonable by reading the surface language.