This is assuming that ChatGPT had everything needed to do the work. If the plumber was asking specific questions, based on their previous experience and knowledge about what needed to be done, the sister might not have been able to get the same result from her use of ChatGPT that the plumber received.

Experts look things up all the time, because no one can hold all the knowledge of a field in their head. Being an expert means being able to know what to look up and how to use the information retrieved from looking something up.

In the plumber example, ChatGPT is going to tell them to do things using the terminology that plumbers know, and tell them to do tasks that plumbers know how to do. The sister would have to continually look up more and more things about how to do basic plumbing tasks, rather than just looking up particular novelties.

Yes, this is why I mentioned comparative advantage.