It's a fair question. At 5v5, the Bruins spent 1797 mins ahead, 1325 mins tied, and 727 mins behind. Obviously they spent more time with a lead than any other team in the league. But that doesn't actually really change the main advanced stats very much, except in one regard. In terms of league rankings, situationally they were as follows:
Leading: 10th CF%, 11th SF%, 7th SCF%, 10th HDCF%, 10th xGF%.
Tied: 11th CF%, 5th SF%, 10th SCF%, 12th HDCF%, 7th xGF%.
Behind: 12th CF%, 5th SF%, 3rd SCF%, 4th HDCF%, 3rd xGF%.
Their numbers when games were tied are still not particularly special - good, top-10 in the league for sure, but nothing more than that. Mostly look much the same as their overall figures I posted previously. The interesting thing is when they were leading it didn't change too much. Yeah their corsi and shot counts slipped a bit as you would expect, but they were still out-chancing their opposition and putting themselves in good positions to score at about the same rate as when games were tied. Which rather suggests that being in front didn't change too much about how they went about things.
Where the Bs really excelled was when they were trailing. Really good numbers there around their ability to generate quality scoring chances and volume of shots. Still not league-leading, but certainly right at the pointy end.
I think then that your point is generally valid - no doubt being in front a lot had an impact on the Bruins' advanced stats and their numbers when trailing probably give some decent indication of the high level and elevated offensive potency they could reach quite consistently when they needed to. But even these figures are still not especially outstanding, and when considering both these and the tied-game stats, the indication is still that Boston's general play when all-square or chasing the game was very good rather than absolutely elite.
I'll throw in one more stat I think is super-impressive and relevant: the Bruins' SV% when trailing in games was .959. That's ridiculous. When the going was tough Swayman and especially Ullmark kept the team in the hunt and within striking distance of opponents time and time again and gave them opportunities to get back into and win or tie games well beyond what you could reasonably ask for. The goalie factor was huge for us.
I don't want to oversell that or any of this analytics stuff. Clearly last season's Bruins did an exceptional job. I'm just saying that when you look a little deeper, the team's play was not quite as dominant as might appear at first glance, or perhaps more accurately, it was dominant at least partly due to some significant factors that cannot easily be replicated, even if the same personnel are in place. It's not to be negative, just cautious.
However, Krejci twice led the playoffs in scoring, just wasn't that type of center in the regular season.
