Well, by factoring the positional changes you mentioned......it tells us more about the players they moved, rather than Talib's ability. The Patriots have finally, hopefully given up on McCourty at CB. He is a terrible CB. Arrington is a special teamer. He is a nickel at best. He should not be a part of the starting D-backfield.
McCourty has certainly looked better at FS than at CB, but even at CB he improved from last year's dismal performance too. I don't have the exact same opinion regarding McCourty's CB skills, but that's okay because the truth likely lies somewhere in the middle of our two opinions.
One thing you may want to consider is that Arrington is much, much more effective at the star/slot position than on the outside. When he is able to cover closely to the player before the WR gets some ground on him which adds to his weakness on speed, he does a very good job of covering that WR. Keep in mind that Arrington helped to hold Victor Cruz to 4 catches for 24 total yards in last year's SB, and he is one of the better WR's in the league. We also saw him completely shut down Devon Bess in the MIA game.
Arrington should be retained for a reasonable salary due to this factor alone, not to mention the fact that he has superior knowledge of the defensive system here, which should not be taken for granted. Unless they can sign someone better for the same kind of money, I am hoping that Arrington is brought back for the slot role. If we can avoid any significant length of time seeing him on the outside in the base, that would obviously be even better...
Here is a writeup regarding that particular subject from about 6 weeks ago:
Kyle Arrington flourishes as Patriots’ nickel back - Patriots - Boston.com
And another:
Kyle Arrington Has Been Able to Excel in Slot Role Since Aqib Talib Joined Patriots | New England Patriots | NESN.com
If Talib leaves, you could argue they need a complete overhaul once again minus Dennard, who may have some promise.
I don't think they need anything close to an overhaul. I think that the safety and CB positions are both ONE player away from being in the best shape they've been in for awhile. I'd say one player in the starters role, and one more in the backup role. That would be ideal. Dennard will be able to start the entire season, rather than the second half. Ditto for McCourty at FS. No more P.Chung is the 3rd aspect that is positive. We should have better depth at safety with Wilson and Gregory battling for the #3 and #4 spots, and both are better in those slots than what we've had.
We are really one halfway decent man to man CB and/or a better option alongside McCouty away from having a very capable secondary. Also keep in mind that Talib only played in about 1/2 of the snaps when the secondary looked much better through the stretch, so those changes showed us all what they are capable of, not to mention that it certainly does not solely depend on Talib alone.
Even if they can't reel in a high priced FA in the secondary, they can spend a high draft pick, have some progression from the young players they already have (Wilson, Dennard) and
maybe even finally see some competition from Dowling to boot. They can also address the situation with some seasoned vets for depth and competition who will not cost nearly as much. This secondary is on the way up, and isn't playing in the soft zone scheme anymore. Of course that also goes hand in hand with our front seven, who is playing more aggressively, so hopefully that will continue.