> Why should I hire a dedicated writer if I have people with better understanding of the system?

Many engineers are terrible at documentation, not just because they find it boring or cannot put it into words (that's the part an LLM could actually help with) but because they cannot tell what to document, what is unneeded detail, how best to address the target audience (or what is the profile of the target audience to begin with; something you can tell an LLM but which it cannot find on its own), etc, etc. The Fine Article goes into these nuances; it's the whole point of it.

> "Write a manual for air travel for someone who never flew. Cover topics like buying a ticket, preparing for travel, getting to airport, doing things in the airport, etc"

Air travel is a well-known thing, surely different from your bespoke product.