Earlier quoted context omitted.
There's way more human input in the training data than in the prompt is my point, many orders of magnitude more. Of course there needs to be something to start some chain, but that's like saying a human needs to press "deploy" or "start", it applies to any tool. Even a perpetual motion machine needs someone to start it.
And your brain also has way more training data (all the knowledge you gained, all the art you've seen) than what you yourself produce as "art".
Not really unless you have perfect memory. What people do is learning rules and breaking them. The rules exist outside of your mind, you're just trying to conform in some ways and distort them in others. You do not blindly copy what came before. When drawing a portrait, there are the rules of anatomy, perspective, colors and light, and your medium of choice. A style is a particular combination that you know works, but you still have to know the rules in the first place. You study masters to learn what is and what is not important in those rules, not to recreate their works in details. I've not heard of any art classes that train you by copying everything that has been produced.