I don't think AI will create a coin superior to Bitcoin. However, various tasks can be performed with AI. For example it can develop a more successful bot for trading. When trading, bots usually trigger each other, that leading to sharper ups and downs. Since the amount of circulating coins used for trading is decreasing daily, this could pose a minor threat. We may see more volatile price movements. Other than that, I don't think AI will pose a serious threat to Bitcoin.
AI with reinforcement can be good at trading and creating such a bot for trading can be helpful but it's still risky as bot might make trading mistakes and the one who used the bot for trading might end up losing money if the market dumps pretty badly but I believe it's highly possible to have a bot that performs really good even if market dumps and that type of bot can be very useful for the ones who believe in DCA + Dip buying. I also agree with you that AI is not going to create a coin that's going to be better than Bitcoin. Even if it creates a coin that's better than Bitcoin I won't consider that coin over Bitcoin.