I think you overlooked a number of things about hockey in the 1990s. For one thing, the "trap" didn't just appear out of nowhere in the 1990s. In fact, the Montreal Canadiens had adopted and perfected it more than 25 years earlier (which explains why the Devils became the standard-bearer for the neutral-zone trap in the 1990s, with Montreal Hall of Famers Jacques Lemaire and Larry Robinson serving as the core of their coaching staff).
Montreal was a dominant offensive team when they played the trap, and the Devils were a very underrated offensive team as well (just look at their offensive numbers in those five or six years between 1994 and 2003 when they were legitimate Stanley Cup contenders).
What really brought about the decline of hockey in the 1990s was expansion in that era. There simply wasn't enough talent to fill the rosters of all those teams, so the NHL ended up with so many players who should have been third-line and fourth-line forwards and #5/#6 defensemen creeping up on rosters and being forced to play key roles on many teams. That's not going to change unless the NHL starts cultivating a heck of a lot more talent, or until the NHL seriously considers contracting to a 20-team or 24-team league.
You are correct, what I meant to say was the maturation and universal adoption of the trap.
Not everyone used it until they realized that it produced more “competitive” results with more meager talent, then when it became universal, it killed the game (for me, at least)
And hey...Boston used it more than anyone.