Programming is also applied physics. But understanding the kinetic forces behind typing is no guide to improved programming.

To say that learning a field is useful is to say that knowing these abstractions is useful.

Much of Haskell's "category theory" is a reuse of terms. Replace Monoid by Appendable, Monad by Composable, Functor by Runnable, etc. and most programming languages are "category theory".

This says little about whether knowing the field of category theory will be useful to programming. Indeed, I think there's a good argument to say Haskell programming is much harmed by it.

If its authors hadnt used their knowledge of category theory, but rather named the abstractions in more ordinary terms, the language would be more useful to more people.