AI can write business plans even better than humans. The major problem is that humans are still learning how to write prompts for it. Secondly, the more details and figures you provide, the better the response will be. And finally, you must realize that AI makes mistakes and provides incorrect data quite often. So you still need a human to verify everything after it and hold responsibility for that. You can't tell your investors later, 'Oh I am sorry, it was AI that made a mistake!'. As an HR partner for one of my businesses, I tried to make it write a company HR structure and CRM use one day. The result I got was quite good, but not exactly what I expected. For instance, it suggested using many small CRMs for each task, while I used  https://www.goodday.work/ and it saved me a good deal of money later. Because it ensured great communication within the team and kept all data accurate.