It is if they're competent but 'master of none' completes the quote so what you end up with is either a not very good defender who sees himself as a winger or a winger who is being forced to defend and isn't very good at it which also leaves hims stranded at the wrong end of the pitch if we break, e.g Nemane who also couldn't head a ball.
Unless we can unearth some hitherto undiscovered talent, I remain unconvinced by wing backs personally, they are neither one thing or the other.