And the problem is more - how can an LLM tell us it doesn't know something instead of just making up good sounding, but completely delusional answers.
Which arguably isn't about being smart, and is only tangentially about less or more (external) knowledge really. It's about self-knowledge.
Going down the first path is about knowing everything (in the form of facts, usually). Which hey, maybe?
Going down the second path is about knowing oneself. Which hey, maybe?
They are not the same.