The preconcept that dynamic languages are more productive is just an illusion because you can easily take shortcuts that will hamper your progress in the future. A proper typed language with HM type inference has the ability to mostly avoid writing the types with the guarantee that the compiler will catch most of the pitfalls. And if you don't do any logic error pretty much every time your code just works. Saying that in a million line application Python is a better choice than F# or Haskell it's frankly ridiculous in my opinion.