Your conflating the medium with the source of the message in this analogy.
Writing and oration are two different media, the question of which is preferable in which context is completely unrelated to LLM authorship.
If "the purpose of writing is to convey ideas" (which I largely agree with), which ideas are being added between whatever you prompt the model to convey and what the model conveys? Are you proposing that an LLM can extract some meaning from your initial prompt that a human being couldn't?
> Are you proposing that an LLM can extract some meaning from your initial prompt that a human being couldn't?
No, I’m asserting that an LLM can help formulate ideas in a coherent, understandable way. You can give it a brain dump with a rough outline for an argument and it fill in the details. If the argument isn’t to your liking, you can try again. But the end result is basically equivalent to the human-written equivalent.