Indeed not. The useful point this article makes, I think, is that if you're a good Haskell programmer and a competent C programmer, you can produce working code

Indeed not. The useful point this article makes, I think, is that if you're a good Haskell programmer and a competent C programmer, you can produce working code in both, but you can still produce better-performing code in Haskell. Essentially, the lesson is that there's little point writing code in C for performance unless you're good at it. If you can write good-enough code in a higher-level language that you're happy with, you might already have reached an optimum.