A work ethic is not a factual thing, it is a principle. You mean his work schedule. Compared with, say, Charles who is not parent to young children and known to be a workaholic.
William probably just wants to be more of a hands on parent in the early years, unlike Charles or The Queen. History suggests that’s a good thing.
I mean, I don’t know, as I don’t know him. Maybe he is lazy or maybe it is an easy form of criticism.