It's an interesting debate, because it's almost impossible to know for sure whether it's the players that are bad or the coaching is bad. It sounds like McCarthy has made up his mind, though, with his comments about the defense needing more playmakers.
TT's draft and develop strategy can definitely work, and I'm not one clamoring for FA signings, but relying on the draft exclusively means the drafting has to be exceptional. Bad drafts are not something a guy with TT's strategy can afford.
Dom Capers defenses going back 7 years have record setting poor performances.
This is really the deciding factor for me. There are plenty of bad defenses in the league, but those are generally universally bad against all opponents. The Packers seem to be fine on defense against less accomplished offenses, but top-tier offenses can make them look embarrassingly bad. Roethlisberger's 500-yd game, Kurt Warner in the 2009 wildcard game. Peterson gaining 400+ yards in 2 games last year, Kaepernick in last year's playoffs. Bouldin in the opener.
It's just my instinct, but that just seems like a coaching problem to me. As if there's a major weakness in the defense, but one that can only be exploited by top offenses. There are enough crappy teams to get the Packers a division title, but it's hard to imagine the defense holding it together enough to get through the playoffs.