"It's an unreasonably high standard to require of LLMs": LLMs are already vastly beyond your 5 year old, and you and me and any research mathematician, in knowledge. They have no greater difficulty talking about advanced maths than about Spot the Dog.

"It's a standard we don't require of other humans": I think qualitatively the same capabilities are used by all humans, all the time. The special thing about novel mathematical thinking is that it is verifiable, requires genuine insight and is a text generation task, not that you have to be able to do it to be considered intelligent.