The Leafs currently sit 10th in the NHL in shots against per game, meaning there are 22 teams who allow more. included in those 22 teams are Florida, Colorado and Minnesota. Expected goals is a metric that takes into account the location of the shot and the percentage of shots from that location that end up in the net. A shot from the side wall, for instance, will have a much lower xG value than one from the slot. With this metric we can see whether the shots the Leafs D do give up are from high danger areas or not. As it turns out, the Leafs sit 5th in the league in Expected Goals Against. Much better than public perception.
If the Leafs have an issue this season, it's in net. Petr Mrazek and Jack Campbell have both been through injury and inconsistent play. Any time the Leafs are able to get goaltending somewhere near the league average, they win. A lot.
Looking at the penalty kill, the Leafs are 5th in the NHL. How many bad defensive teams have a top 5 PK in the league? The Leafs also lead the NHL in shorthanded goals, meaning not only are they playing good defensively, they're also able to turn sound defensive play into good offensive chances.
Now, lets talk personnel. Just 2 years ago, the Leafs' top 6 on D looked something like:
Rielly-Ceci
Muzzin-Holl
Dermott-Barrie
While that iteration of the team's D corps may have been weak, it was made worse when Muzzin went down and was replaced by Martin Marincin. This year's defensive group, however, is vastly improved. When fully healthy, the Leafs will be able to roll out:
Rielly-Lyubushkin
Muzzin-Brodie
Giordano-Liljegren
I have Liljegren in the top 6 here because since being partnered with Giordano his game has elevated far beyond anything we've seen from him in the past, and Sandin hasn't looked great in his limited minutes playing the right side. This leaves Rasmus Sandin and Justin Holl as injury insurance. That's a well balanced, strong top 6 with what is probably the best 7-8th defencemen in the league.
Having said all this, I think its time to put to bed the narrative that the Leafs defence corps is bad, or lacking depth. In fact, I can't recall a better group of blueliners in my lifetime than the one we are watching right now. The Leafs' D is good, and we should appreciate what we have now rather than pretending that it's not.