Criticizing Sullivan for having great rosters and then saying Bowman was the best is kind of rich. Dude coached nothing but HOF players and they hated him so much they chased him away after the worlds biggest choke against NYI after only 2 seasons. But comparing the rosters with Bylsma vs Sullivan is an interesting question.
Pens had 5 seasons under Sullivan where they were real Cup contenders in my opinion. 16, 17, 18, 21, 22. Won in the first two, 18 was bullshit, they would have easily won the Cup if Hornqvist, Hagelin, Malkin, Kessel, Brassard weren't all injured. 21 they dominated the Isles and Jarry just gave the series away egregiously. 22 they dominated the Rangers but they were playing a non NHLer in net.
Bylsma Pens were true contenders in 2009, 2010, 2012, 2013, and 2014. 2010 and 2014 is debatable, but those team should have at least went to the conference finals even though they probably wouldn't have beat Chicago or LA ultimately. The flame outs for the Bylsma Pens were more obviously coaching related than Sullivan's teams - especially 2012, 2013 and 2014.
I think ultimately Sullivan's best teams were better than Bylsma's best teams but Bylsma had the biggest star advantage in the league and couldn't get a win past the second round after the Cup in his first season where he obviously won because he simply wasn't Therrien.
Sullivan legitimately had the 2016 team change hockey, and then he won again the next year without Letang in what was the best coaching job in Pens history. Yea, he got stale and high on his own supply but Bylsma won ONE CUP by not being Michel Therrien. Sullivan actively coached his way to a back to back, when it hadn't been done since the 90's.