Doubtful. I read a lot of forum posts, as I maintain a popular OSS project. And, I read a lot of books from the before times. And, I read a lot of LLM prose, because I use them every day for coding and various assistant type tasks. It's still pretty obvious when an LLM writes something.

I even did post-training on Gemma 4 (a small model which has very good prose for a model, especially a small model) to try to make it able to write more like me, purely as an experiment to learn how training LoRAs works, and using data that I know is ethically sourced. It still distinctly writes like an LLM, with a few of my annoying quirks baked in: Inappropriate use of ellipses, too many parentheticals, occasionally dismissive tone. But, it can't stop doing the LLM things, either, without becoming incoherent.