I think Carmack is conflating FP with good abstractions.

Haskell abstractions are often good because they flow from category theory and there are usually well established mathematical laws associated with them. I'm thinking of the "monad laws" and the "monoid laws."

Mathematicians tend to create abstractions if the abstraction satisfies coherent and provable properties. Programmers tend to be less rigorous about what and how they abstract.

There is nothing about C++ that prevents making good abstractions. It's just the culture of the language. Industry programmers are taught to not duplicate code and to keep functions short but they are not taught the fundamentals of what makes a good abstraction.