Subban is a good defensive player, it's just that he is prone to make the stupid mistake from time to time. In Montreal, he did this more frequently but now that he's in Nashville and understands his role as a shut down guy, these mistakes are becoming increasingly rare. An example of this would have been that 360 no-look behind the back pass he attempted the other night that was picked off
Karlsson has improved on the defensive end for sure and is by no means a liability, but he is prone to playing loose at the front of the net. With his body type, he is built better for being the offensive workhouse that has gallons of endurance on reserve to rush up the ice. But he sacrifices pure strength and often leaves guys wide open at the front of the net as he tries to block the pass or shot. This works oftentimes but when it doesn't it can be fatal. An example of this would be the overtime goal in game 5 of the boston series.