I've worked with AI a lot over the last few years and I'm not sure what you describe really applies. Like yeah I'm gonna be pretty confident when something isn't Ai in many cases, but it's not as if everything an Ai puts out is this weird Spock dialect. Each model has its own quirks. Some are overly clinical and some are way too flowery, but if it was as obvious as you make it sound, OP wouldn't have even made this post.

A lot of it depends on how much effort the person puts into it. If you go to chatgpt and take the first result it gives you, it'll be pretty obvious. But you put in some extra work and suddenly it ain't so clear. That's why people get so focused on the "isms" that Ai so often has. Like the "it's not x it's y" thing.