Not a part of that group, but I think this is a false narrative. 20% might be accurate, or it might be a bit high even. But it has nothing to do with `top` or `bottom` performers. It's purely to do with exposure to functional styles.
Learning Haskell first doesn't make you a top 20% developer, much as I'm sure HN in particular will want to argue with me on that point.
All I'm trying to say is: there's not an intelligence spectrum of `imperative` to `functional` with `object oriented` in the middle. They're different, and many who learn one first struggle with the others, but that doesn't mean they're lower performers in what they do know than the ones who can talk about currying vs partial application.