Or you could watch the games more often and see what kind of defensive breakdowns plague the Leafs and when they happen.
A classic example of which is a scoring line getting caught at the end of a shift at the attacking end of the ice, resulting in a lengthy siege getting cycled to death (no shot on goal) followed by a miscue in front of the net, puck squirts out to the high slot and ends up in the back of the net. Doesn't really show up in a CF% that looks too bad on paper but is ugly, predictable and happens too often.
All teams suffer those kind of breakdowns and what makes corsi so effective in tracking possession is that there is eventually at least a shot at the net when a tired scoring line is out there, often multiple shots. taking that further down the rabbit whole you also have scoring chances against and ultimately high danger chances against (those high slot shots, etc..)
Last year, the Leafs were:
5v5 Corsi against/60: 59.33 (27th in the NHL)
5v5 shots against/60: 32.66 (27th in the NHL)
5v5 scoring chances against/60: 28.27 (25th in the NHL)
5v5 high danger chances against/60: 10.69 (18th in the NHL)
Hainsey had started to show his age, Gards back started to go in early Jan. and until Muzzin came along to stabilize the D, they had some brutal defensive months in the middle of the season. Freddy really had been carrying the team for much of the season but his drastic dip in play the last third covered up the fact Muzzin had made quite the impact on the depth of the D just when we needed it.
So far this year:
5v5 Corsi against/60: 55.53 (21st in the NHL)
5v5 shots against/60: 30.67 (19th in the NHL)
5v5 scoring chances against/60: 24.52 (16th in the NHL)
5v5 high danger chances against/60: 8.47 (12th in the NHL)
Even with the two new faces in the top 4 and no Dermott and despite one of the more brutal schedules to start the year, you can already see how much improved the D has been at preventing scoring chances while still being one of the top offensive teams in the league. I'd like to see a larger sample size of course but we should all be optimistic I think.