Kirk Muller runs the powerplay. Despite only winning 29 games, Montreal had the 13th best powerplay in the league. The only teams in the Top 20 powerplay with less than 40 wins were the 6th place Islanders (35), 9th place Canucks (31), and 20th place Sabres (25). Out of those teams Montreal had the least powerplay opportunities (though were only separated by 2 with Vancouver) at 245.
In 16-17 the Habs were 13th again, albeit with a lower percentage. But they also were 27th in opportunities. In 15-16 the powerplay sucked and was 25th (pre-Muller) but also was 11th for PP opportunities. Between 12-13 and 15-16, the Habs were 6th in PP opportunities and 23rd in PP. 16-17 to 17-18 (smaller sample size I know) we're 23rd in PP opportunities but 11th in powerplay. You can draw your own conclusions on some of that. I should add that between 12-13 and 15-16, Subban was 4th in PP goals and 1st in PP points with Markov 11th in PP goals and 4th in PP points so it wasn't like the firepower wasn't there. Muller is making a serious contribution to the team in the way they play the powerplay in ways the crappy coaches Therrien brought in before Muller couldn't.