I think having Singetary back would help with blitz busting screen plays. Make the other team pay.
That said, I am still not 100% sold on NE's defense. YES they have done well, but I have lots of "buts"
AFC Title Game: Torched in the 2nd half by Mahomes and Reid and only won because Dee Ford lined up Offside to negate a Brady game ending pick
Super Bowl: held what was then a slumping Rams offense to 3 points without their best RB and WR
Week 1: Big Ben with a destroyed elbow
Week 2: Miami
Week 3: Jets 3rd string QB and banged up RB
Week 4: Young QB who has been up and down and making mistakes. Also were 1 yard away from blowing that lead, even with 4 picks.
Week 5: Colt McCoy
So yeah, because they are NE everyone will go GAH GAH over them. But really, the only time they have been tested they got lit up and were saved by an Offside penalty and a coin flip in OT.