Since Q and JC have coached about the same number of games I've been looking at some underlying numbers for each stint. Although it's way too early for any kind of evaluation, everything seems to suggest Q and JC should have had around the same record. Basically, the main differences were luck, goaltending, and Q getting to play the Blues two extra games.
At 5on5, expected goal percentage was 44.76% for Q, and 45.77% for JC. Both of these are terrible, and reflective of the talent level, but things may actually be improving process wise under JC. If you just look at his last 7 or 8 games, the numbers look even better. Although still well below 50%. The luck factor is also kind of reflected in the goal differential during each stint. Q was expected to be at about -6 5on5, but was only -3. JC also had an expected differential of -6, but they were -11 during his stretch.
Part of the reason for the difference in expected goals seems to be JC doing a slightly better job at both generating high danger chances for, and limiting chances against. Not to any great amount but it basically comes out to half a chance more per game, half a chance less against a game. The hdcf% went from 43.64 to 46.33. Again still terrible, but an improvement.
Pace of play may be the biggest difference between the two. Q has been more run and gun the past two seasons. This year they were near the top of the league in attempts, but at the bottom in the amount they gave up. Under JC, they've been middle of the pack in both. Q had a slightly better shot attempt share at just over 51%. Under JC it`s just over 50.
Goaltending issues have been more about the types of goals given up lately, but the save % was higher under Q - 91.41 to 90.76 (just 5on5). There was a bigger difference on the pk, with Q getting 86.75 and JC 82.09 (near the bottom of the league). Shooting % has been low for both teams - 7.24 (Q) and 7.36 (JC). Both teams took about the same number of penalties but the JC team is much better at drawing them for some reason. JC is +2 penalties drew versus taken, to Q's -12.
Looked at special teams too, but it seems way to small a sample size. PP hasn't changed too much, although there has been a pretty big increase in shot attempts under JC. A lot of it I think is coming from the point. Q actually had a slightly higher expected goals per 60, but it`s not much of a difference. There was a bigger difference on the pk. Basically we should be giving up one more power play goal against every 15 game or so under JC. Weirdly, we're also expected to score about 1 and a half more short handed goals over that same 15 game stretch under JC. They have seemed a little more aggressive in terms of forcing turnovers and and taking chances at times, but I didn't expect that much of a difference.