I'm not a stat expert, but I just don't get the importance of that stat. If it's such a good indicator of a quality defensman, how come the top fifteen defenseman in that stat isn't littered with the best defensman in the NHL? Karlsson is the only name on there that's a legitimate top defensman, and everyone's played about the same amount of games except for a couple guys.
The stat is imperfect, but it's not useless. I wouldn't put any stock into it this early in the season, especially for Barrie who has only played 5 games. But if you start looking at a full year's data it starts to make much more sense.