I will even add a 3rd layer, the man delivering Capers the Personnel that he is asked to coach and develop, Ted Thompson.
They (TT, Capers, players) all are interconnected and it's a circular connection, if that makes sense.
TT's job is to look at the defense and see what it needs, while keeping in mind what Capers needs and what type of player fits those needs and his coaching Style.
Its up to Capers to express those needs to TT and then take what TT gives him and use his abilities to coach those players.
It is up to the players to learn what Capers is coaching them and translate that onto the field. Meanwhile, the circle forms, TT is evaluating each player to determine if its a successful fit.
Simplistic, but complex all at the same time. Can you cut one cord without cutting the other? Sure, Capers could be fired and replaced, but TT still still needs to find players that a new DC could coach and have success with. Personally, I think there has to be a combination of either cutting one cord (Capers) and a cutting or at least modifying of the other (TT). Capers may not have all the guys he needs to successfully build his defense, but this has been an ongoing issue in Green Bay for too long. His defenses are statistically terrible against top 15 offenses in the regular season and even worse in the Playoffs. But whoever they bring in to replace him, has to have a voice with TT and the players he drafts, trades or signs as free agents. TT needs to be held accountable for his lack of giving Dom enough to work successfully with and if he isn't willing to modify the way he is operating at GM, he should go too. The 3rd cord, the players, all can't be fired, but better ones can fit in as they are obtained or developed.