LLMs have zero accountability when it comes to fact checking. They have been shown time and time again to just make shit up.
Factual sounding bullshit is absolutely not good, and definitely not "better than humans" for a system that aims to be a fact repository. Sure, they can be a tool to help with writing, but only if the author 100% knows what they're talking about and just needs help with editing.
People who paste raw LLM output into Wikipedia generally do not know what they're talking about as well as they think they do.
Also, it is not "downright banned" - it gets a warning and flagged for review because the frequency at which LLM copy-paste is bullshit is too high.