Years ago I observed a single word/term that used more or less the description above, but I have been unable to locate or remember it since then. I am certain that it was a single word, and thus "jack of all traits and master of none" and other popular phrases don't fit. Any help you can provide would be much appreciated!
Merriam-Webster says a dilettante is a person having a superficial interest in an art or a branch of knowledge. To get the "Jack of all trades" sense you could say "He is a dilettante in several fields."