I think average people can easily spot AI because it mimics literature and most people don't spend that much time with literature. However literary critics should be fooled way more easily because what we perceive as stiff fakery is their daily bread and butter. People do write like AI, just not the people we are exposed to mostly.

I remember riding a train and there were other two passengers talking. And they talked in so obnoxiously literary manner I was cringing all the time. Those people were just reading a lot of high literature and their speech patterns aligned. For an average ear it doesn't sound good. And AIs, the smart ones, don't sound good in a very similar fashion.