As a test I ran some questions through ChatGPT a few weeks ago; both popular ones and just some random ones from the homepage (including some not-very-good questions). In only one case would I say that it was "good enough" to post. All the rest ranged from "mostly correct but with huge omissions" to "used 5 paragraphs to explain what could be one or two sentences" to "this is not even remotely correct in any way, but at a glance it actually looks kinda correct". The "looks kinda correct" can be pretty misleading, because there have been a few answers where I went "wait, is this actually a thing? I didn't know about that!" and when investigating further it turned out it wasn't a thing at all and ChatGPT was just trolling me.

- Humans actually try to answer the question at hand, whereas ChatGPT is only auto-completing text. This might lead to similar results in a lot of cases, but the goal of ChatGPT is not to produce correct SO answers.

- Related, humans will (usually) back off or correct answers if errors are pointed out to them. ChatGPT (at the moment) doesn't.

- Humans will (usually) not attempt to answer questions they don't feel like they are qualified to answer. ChatGPT will.

I'm not saying that SO is/was perfect as-is, but ChatGPT is - in my opinion - overall not likely to improve SOs quality as of now. Since it is currently banned on SO, it seems like this is not only my opinion.