that's fair and you have highlighted a good limitation. but we do this all the time - we try to understand the author, learn from them and mimic them and we succeed to good extent.

that's why we have really good fake van gogh's for which a person can't tell the difference.

of course you can't do the same as the original person but you get close enough many times and as humans we do this frequently.

in the context of this post i think it is for sure possible to mimic a dead author and give steps to achieve writing that would sound like them using an LLM - just like a human.