I don’t think Belichick will ever run an overly aggressive defense, it’s just not his style, and really it just comes down to having better players so you don’t have to manufacture pressure.
When the Patriots’ defense was at it’s best last decade, they could get pressure with just four guys and as a result, the secondary always looked better than they might’ve really been (with the exclusion of 2003, when the secondary was the best it ever was).
To me, the keys are generating good pressure with Ninkovich-Kelly-Wilfork-Jones, and allowing Mayo, Hightower, Spikes and Collins to make the plays. Having their entire defense return nearly intact bodes well, especially in a system like Belichick’s that is all about communication and reading route combinations.
Ideally they’d love to be able to run man-to-man on the outside, and with Talib and Dennard they should be able to.
The defense should be better from the front to the back, but it’s less about versatility and more about just having better and more experienced players who can win their matchups.