The problem with this argument is that people do the same thing, we’re not that great at brainstorming either. When we brainstorm in groups, we’re just bringing multiple points of view together. The more data LLMs are trained on, the more viewpoints it might be able to bring that you haven’t considered.
That said, LLMs and all NNs so far are built to interpolate, and they are bad and have unbounded error when extrapolating outside their training examples. That is a good reason to not expect today’s AI to come up with new ideas.