A depth player is a 13-14th forward or 7-8th Dman. If this is your view of Z then I disagree, Z is a everyday player on any team.
I think that's a bit overly obstinate. A depth player is not someone who's in the press box more often than not. Those are just "extra" players. A depth player is generally regarded as anyone beyond the top two scoring lines or top two pairings on D. And really, Z is more of a bottom pairing guy on a contending team. He is, at best, a #4 defenseman, and frankly I think that role sometimes overwhelms him.