It's probably possible to prompt an LLM into writing well, but most LLM writing that I've seen is poorly structured (e.g., the paragraphs in this post feel like strings of punchy marketing phrases), and the LLMs are too good at sounding like they're saying a lot while saying very little.

Plus, if a human puts the effort into writing something, that signals to me that it's worth something, because human time is much more scarce than LLM time.