I have a different opinion on the defensive issues. Something to note is that few people understand the defensive dynamic. Defensive football is without question the archeotype for cohesive team sports. D Line effects backers, backers effect secondary, and vice versa down the list.
I am likely the most vocal criticiser on this forum that Dean Pees has. That damn cover 4 or any derevation thereof is cianide to any defense. That said, unless a blitz can finish it is effectively useless. As the linebackers shoot gaps, they vacate areas in a defense. Most offenses are step based in the passing game. If a blitz does not reach the QB before the passing step, there will be a significant gain. This leads to a discusssion on rushing the passer.
Blitzing and pass rushing are the most cerebral components of defensive football from a player's standpoint. Blitzing is fundamentally about snap count timing. Obviously, as the levels of play advance, the cadence becomes more nebulous. The ability to time this comes only from pre-game study and in-game adjustments. This is clearly a veteran skill set. Yes, there are athletic exceptions to any rule, but from a practical staffing standpoint this is the most critical component of effective blitzing.
Accordingly, if the rushers do not execute, the secondary must give a significant cushion. It's the choice between a slow death and immediate scores. I think this is the reason behind the off coverage. The great Patriots teams predicated upon defense had a combination of great pass rushers and press corners. The best press corners cannot play their brand unless there is an effective blitz and vice versa.
While I think that the unit could stand better playcall, the real issue is veteran staffing. This is the best secondary NE has had since '04, but without the staff and creativity, it is doomed to schematic mediocrity. Go get Peppers.