I find that argument to be suspect, perhaps worthy of one "?", but not "???".
One cannot laud Thompson for (1) signing his own; (2) conserving cap in order to do so, (3) eschewing free agency acquisitions as risky and (4) cycling out the merely serviceable, the old and the injured in favor of youth, and then wonder why the departing Packer free agents have not seen particular success.
By the time Thompson's better defensive players are let go, they had aged or have experienced career-threatening or career-ending injuries.
Let's take the 2010 defense as an example, the most talented and effective group during the Capers era:
Raji - He's still around..."keep your own" perhaps beyond the sell-by date.
Pickett - He was let go after advanced age and knee issues in the season prior to his being let go...another "keep your own", also perhaps beyond the sell-by date.
Jenkins - That was one FA loss that looks like a mistake in retrospect. He went on to play well in a disfunctional Philly defense with no adequate replacement.
Hawk - He played his best in 2010 and got a nice contract. A good player in his prime, kept beyond the sell-by date.
Bishop - He was a quite welcome addition in 2010; a guy who played well and was rewarded with a nice contract; a guy who looked like he'd be a long term stalwart at Sam backer. He was let go after a career-threatening injury from which he has yet to recover.
Matthews - Still with us, of course. Paid to stay with the highest contract in history at the time for a 3-4 OLB, emblematic of "sign your own".
Walden/Zombo - Every defense has some serviceable players, and these guys are among the few in this unit that qualify. Walden got a nice contract from Indy, and he's been a starter for them. Did he play close enough to the value of that contract at the time? Perhaps not, but not so far off to isolate it as an example of the issue at hand.
Woodson - He got old, was no longer a cover corner, did not take immediately to the safety position and had a hefty cap hit left on his contract. Nobody would have expected him to have much left in the tank. And yet, he made the Pro Bowl as a safety last season.
Collins - Career ending injury.
Peprah - Really? He was a rent-a-player in the serviceable category when Burnett went down. So, when Thompson signs some vet FA wide receiver for this season and then lets him go a year or two later, are we going to call that a Thompson failure?
Shields - Came on late in 2010, and is still with us with a high price tag...another "keep your own".
Williams - He hit the +30 mark with room to spare and he's not been the same player since he had the shoulder nerve damage. The book is open here. We'll see how he does in Cleveland relative to what they are paying him.