I love a good em-dash, but this page overuses them (nearly 1:1 ratio of em-dashes to commas!) and puts them in places where they just do not belong.

That's very weird, I on the other hand don't remember noticing them or using them before the advent of chatgpt. Maybe it's a cultural thing.

It makes sense that humans would have been using it though, chatgpt learned from us afterall

Same here. The em dash has been maybe my favorite punctuation since at least the early 2000s. All the em dash output from LLMs looks really natural to me.