Someone who learned Haskell intensely for 8 days could very well be more productive than someone who learned Haskell intensely for 80 days. The former probably got a good introduction to the standard library functions and has become familiar with the main classes like Functor, Applicative, Foldable, Traversable. The latter might be too engorged in advanced language features like TypeInType; or evaluating and choosing between slightly different abstractions to accomplish a single goal, like choosing van Laarhoven optics vs profunctor optics.

And I'm not trying to demean advanced type system extensions or van Laarhoven lenses; I'm just reflecting on my personal journey with Haskell. Playing around with the language in this way is similar to playing around with advanced template meta programming in C++. It just takes experience to have the discipline to know the difference and write simple code and be productive.