"The user could have written the code themselves"

Yes, sometimes this is true, but not always.

Note, it's not one prompt (there aren't really "one prompt" any more, prompt engineering is such a 2023-2024 thing), or purely unreviewed output. It's curated output that was created by AI but iterated with me since it goes with and has to match my intention. And most of the time I don't directly prompt the agent any more. I go through a layer of agent management that inject more context into the agent that actually work on it.