You really can't compare how the Packers start to how the Brewers start. At least you shouldn't be in that mentality. Baseball is so different than football. What a team does in April and May is pretty much meaningless as long as they don't lose every game. What a team does in September in football isn't meaningless at all. It's huge.
The Brewers were a collapse waiting to happen even when they were healthy and playing well. The Packers on the other hand are clearly an upstart team with great coaching on both sides of the ball that won 13 games just two years ago without this type of coaching on defense.
People undervalue coaching so much, but in football it means way more than it does in baseball. I know baseball purists won't like this, but football is harder to play than baseball. Coaching is tougher in the NFL than it is in the MLB. It takes a lot of energy to play football. That's why it's only done once a week. The Packers have probably the best overall coaching staff in the division now with Capers and co on board. Not to say that they can't fail as they can, but coaching + healthy players = better defense.
I really think the key to this season is staying healthy. GB does that, they're in good shape.
You take out several starters on every team and replace them with their backups and that team will struggle.