This sounds suspiciously like the average developer, which is what the transformer models have been trained to emulate.

Designing good APIs is hard, being good at it is rare. That's why most APIs suck, and all of us have a negative prior about calling out to an API or adding a dependency on a new one. It takes a strong theory of mind, a resistance to the curse of knowledge, and experience working on both sides of the boundary, to make a good API. It's no surprise that Claude isn't good at it, most humans aren't either.