Whether a person is a “jack of all trades and a master of none” depends on how you define trades. The same person could be a dilettante or a specialist depending on your mental categories.
Take an expert programmer back in time 100 years. What are his skills? Maybe he’s pretty good at math. He has good general problem solving skills, especially logic. He has dabbled a little in linguistics, physics, psychology, business, and art. He has an interesting assortment of knowledge, but he’s not a master of any recognized trade.
Is a manager a master of one trade or a jack of several trades? Obviously if you recognize management as a profession, then someone who is good at it is a master of that trade. But if you don’t have the mental category of manager, what is a manager good at? She knows a little psychology, a little sociology, a little math, she has good communication skills, etc. But she’s a jack of all trades and master of none unless you have a name for her trade.
Calling someone a jack of all trades could be a way of saying that you don’t have a mental category to hold what they do.
Related post: Too much time on their hands