I figured I should take a better look at his games - not just in realtime while watching, but breaking down video on replays, see if the chances were really his fault or not. Here's my assessment of every strong scoring chance against that happened while McCabe was on the ice, against Chicago (he was on for most of the strong scoring chances against):
1) McCabe bobbles the bouncing puck, doesn't position his body to block it either, allows strong scoring chance, is lucky that Woll bails him out. His high level positioning is good, but the details/hands aren't, in a high danger area like this you want to get your body in the way so it blocks the puck if you miss it with your stick
2) Combination of errors on this one. Bad point pass by Gregor, then a bad decision by Klingberg (should've backed off and allowed the zone exit vs. trying to hold the line flat-footed). I think those 2 are mostly at fault, but also don't love McCabe's transition D, does end up caught in no-man's lang a bit. McCabe "meh" but not terrible, Gregor and Klingberg more at fault, although at least Gregor makes a great backcheck to limit the danger of the scoring chance
3) Similar to the last play - McCabe not terrible, but not great either. Bedard beat Klingberg clean off the rush, McCabe defends sort of OK, but not great - he ends up in no-man's land a bit, not really covering Bedard or effectively taking away the pass to Donato. I think this is mostly on Klingberg, but McCabe is at best average here, more like below average. Would also like to see McCabe stop in front of the net here, vs. skating himself out of the play - he would have been in terrible position if there was a fast rebound chance.
4) Pretty bad here IMO, just too big gaps all over the place, too passive and slow to apply pressure a few plays in a row, ending up in a goal against. Though I will say, Klingberg puts him in tough spots again - puts him in positions where he has to be super on the ball with his gaps and pressure just to do OK, and he isn't. This is an issue I see often with McCabe - he's not often badly out of position, but he is often just a step behind the play, struggling to keep up and not applying meaningful pressure
5) McCabe strongly at fault IMO, Lily is in good position to defend the puck carrier (Athanasiou), and the pass to Johnson is the clear biggest danger. There's a number of Blackhawks sort of on the rush, but only Athanasiou and Johnson have the speed and positioning to be immediately dangerous, if the puck goes to anyone else other Leafs will have time to recover and join the defensive effort. It's clear the right play for McCabe here is to cover Johnson, but instead he doubles Athanasiou, leaving the pass to Johnson wide open. Then he's too slow to recover, goal against. I think this is the only goal against that Lily has been on for this season? Knies also could have been better here, but McCabe is a vet dman, I put more responsibility on him to be the last line of defence vs. a rookie winger.
These chances/goals are certainly not all McCabe's fault, Klingberg especially is putting him in bad positions frequently. This made me revisit my thinking that McCabe is worse than Klingberg defensively - I think Klingberg is worse than McCabe on these plays, he's often the root of the problem while McCabe is more often the secondary issue. Will have to keep looking out for this, it's probably a pattern.
However, McCabe does still look pretty bad on these IMO, especially since he's not an offensive guy like Klingberg, if he contributes anywhere it's defensively. This is maybe a below average McCabe game, but not way below average or anything - IMO he has looked similar throughout the Florida series, and through 3 games so far this year.
Overall, breaking these plays down makes me think we should split up McCabe and Klingberg, maybe McCabe would have more success with Lily, but still not liking McCabe's game. It's not encouraging that Gio/Lily have been rock solid together, but in a very rare time where McCabe was paired with Lily, it was an instant goal against that was primarily McCabe's fault.