Quoting: glarson17
Come on, he’s on one of the worst teams in the league which has a -40 goal differential. Karlsson is also currently sitting at -5 but has been on the ice for 11 empty net goals. So the bull +/- argument is useless.
His defensive metrics are not though. They are all much worse than those players I listed. I don't like the +/- stat for the same reason you posted, it's just the easiest to point to. The fact that only two players in the last 25 years have won with a negative +/- (and who those players were) just speaks to how hard it is to win the Norris being a negative player.
Personally, I have him 3rd/4th right now basically due to his offense.
1/2) Fox & Dahlin - Both play great on both sides of the puck. Make a huge difference in their team performance. Play 25+m a night and play in all situations. These are your best OVERALL defenseman (both sides here, offense AND defense)
3/4) Karlsson & Lindholm -- Kinda polar opposites here, Karlsson is great offensively but a hole defensively, Lindholm is probably one of the tops on the defensive side +34 and chipping in at a reasonable rate offensively.
5-10 is a assortment of McAvoy, Hamilton, Morrissey, Makar, Dunn and Chychrun.