Hi Tessa, Thanks for your comment!
What you think may be true, but I'd argue otherwise. I see another two possibilities from what you say.
First, it may be the case that "sufficient intelligence" is way beyond our cognitive capabilities - now and ever. In that case, authorship of texts would remain in the realm of the known unknowns.
Second, and this is what I think, it may be the case that not enough information is contained in the words - whether we look at a word, a sentence, or a whole book - for anyone or anything to arrive at a conclusion as long as the writing skills of the AI are high enough.
That said, I don't think large language models - in theory - will manage to surpass our writing skills in every style or form. Humor, as another commenter pointed out, might be out of reach for these AIs.
It's in the areas they can match us that we should be careful and take special care of our profession.