I think good UI means a user can understand what is possible from the beginning, without learning through trial and error. That’s why AI chatbots are bad UI in my opinion.
That kind of UI makes sense if the interface has a specific purpose, and that's most of them. (Consider a web form.)
Some interfaces are more open-ended than that: command lines, search engines, programming languages, chatbots. There needs to be a lot of varied functionality for the more difficult learning curve to make sense.
