I suppose they really only have to be good at knowing what sort of thing the audience would believe a great thinker would say. As long as the audience does not consist of great thinkers they also cannot know for sure what a great thinker would say.
That's true for unverifiable "talk professions" where there is no grounding and it's all self-referential navel-gazing chatter.
But LLMs are already beyond that in writing code that passes actual tests, proving theorems that are check able with formal methods etc.
The people who still say LLMs are just parrots in 2026 will just keep saying this no matter what, so I don't think it makes sense to argue this point further.