The secondary will be better for the following reasons.
1. Haven't you heard of repetition K. The the Pats have a VERY young secondary. There most experienced plays last season has played only 2.5 seasons and started less that 2 seasons worth of games. (Chung) Arrington and McCourty will be entering their 3rd season of starting. That experience counts. The repetition adds up, and the reactions speeds up. For that reason alone without any personnel changes and the defense would be better
2. The people we are getting back from IR. Dowling and Barrett both would have made big impacts had they remained healthy, getting both back will greatly impact the efficiency and flexibility of the DB's.
3. The players we have added in FA - Gregory is a natural FS who did OK as a SS. I'm not sure how he will be, but I know for a fact, even if he doesn't start, but I know he'll be better in coverage than any S that played for us last season, except for the 8 games Pat Chung played. We also can expect at least one draft pick S as well, and its very likely he can make the same claim as Gregory
So the addition experience will greatly help the CBs (Arrington, McCourty and Moore) Since we had only one legit starting S all year, and he played only 8 games, so I'd be hard pressed to think that things won't be better in that area as well, before all is said and done.