This third part I agree with most.
The Bruins aren't the Kings. They aren't physically, defensively, and goaltending dominating to that extent.
In round one, they looked slow, and the Leafs had no problems penetrating the Bruins defense and pushing the pace.
In round two, the Rangers are limited offensively so the Bruins have been able to get their trademark sustained forecheck.
Against the Pens I think if the Leafs can dictate the pace, the Pens can, and Tukka isn't a bad goalie, but he isn't Thomas or Quick, he can be had.
Plus the Pens have experience and such a deep lineup, they can go big (Glass, Vitale, Morrow, Murray, perhaps Englland). Not a finesse team.
We have the depth to play an offensive or grinding game.
Tukka's shakiness and the Bruins older, tired legs would be exposed more.