Re: the error is in call it "AI" !!!
"Usually those rules were associated with reasons, so an expert system could not only make a decision but also support that with the underlying reasons."
The shortcoming about that is that is can only make the decisions it was given reasoned rules to make.
A real expert, OTOH, will have a degree of understanding that helps them, when confronted with a novel situation, to undertake new reasoning and at least suggest what the best decision might be.