Pittsburgh's and Chicago's D have been brutal. NJ's is better, but still really bad. Toronto can move the puck, but they can't defend for ****.
Montreal's D isn't good, but they've had a lot of bad luck and an uncharacteristically bad goaltending from Price.
5v5 team defence:
They're only 17th in xGA/60 and 19th in adj. xGA/60. They're 10th CA/60 and 23rd in adj. CA/60. They're 20th in SA/60 and 27th in adj. SA/60. And their breakdown in shot danger against is here:
Their penalty kill is likewise pretty bad, but not the worst.
Those are team D stats, but Montreal's D have individually not been as bad as other teams, they've just had worse luck and gotten worse goaltending.
All in all, Montreal's D is still pretty bad, and its definitely worse than last year and significantly worse than it was the two seasons prior to that.