I think part of the reason the Pats D has never been considered dominant nationally is that Belichick doesn't give a crap about yards allowed. It seems to me the fundamentally (extremely basic) philosophy of the D over the Belichick years is to not give up the big play between the twenties and really turn up the intensity in the red zone. Watching that kind of D does not give the viewer the impression of dominance however, when you look up at the score board and only see 10 points allowed you think, "How the hell did that happen? They seemed to be moving the ball well all game."
Belichick doesn't care about extraneous issues, like "dominance" or yards allowed, except for Rushing yardage allowed. All his Defenses produce fewer points for the opponent than the yardage would be expected to produce.
The only reason that Belichick cares about rushing yardage is because it prevents "Bend don't Break" from working,and it ruins the Pass Rush, like it did last season. Judging from the off season efforts, Belichick spent more effort to patch the Rushing Defense than he did on what everyone else was complaining about, Pass Rushers.
Pass Rush will show up when it is 3rd and 8 and not 3rd and 2, as it was all too frequently last season. Still only the very best Teams were able to march down into the Red Zone and score against the Pats. The tougher Rush Defense will stop that, and the Pats Defense will take a giant leap this season.
I like the Defense now. It is probably sounder than any since 2005. It is young, fast, sizable and talented. All it lacks is experience, but even there there will only be a couple of Rookies in that raw situation, unlike last few seasons.
It has been a long time since the Pats had as much secondary talent as they do now. And i can't remember when it had more speed at LB, inside and out. Last year the loss of Seymour downgraded the defensive line dramatically. While not as good as the Big Three in their prime, they didn't have the D line depth that this edition will sport, either.