You don't need a harness beyond Claude Code, but honestly it's foolish to think you shouldn't be building out extra skills to help your workflow. A TDD skill that does red-green-refactoring is using Claude Code exactly as how it's meant to be used. They pioneered skills.
Works better than standard claude / gpt, which doesn't do red-green-refactor. Doesn't seem like slop when it meaningfully changes the results for the better, consistently. Really is a game-changer. You should consider trying it.
I don't think just saying it's an anti-pattern for a multitude of reasons and then not naming any is sufficiently going to convince anyone it's an anti-pattern.
This is in fact precisely what skills is meant for and is the opposite of an anti-pattern, but more like best practice now. It's explicitly using the skills framework precisely how it was meant to be used.