Maybe not top 5, but I can see the Packers in the top 10. They're main problem is they can never stay healthy on that side of the ball. They have some guys that I like though. Young guys like McMillian, Heyward, and Perry showed a lot of promise last year. Brad Jones has been a pleasant surprise at ILB. And I always liked Jolly. I think him returning could help bolster their front. They have some pieces. They do lack depth in key places like LB and safety. But it isn't as far-fetched as some may think....IF they can stay healthy. And that's a big "if"
Being the #1 defense in the league is irrelevant really. You need to be tops in a few key areas though. Just look at the last few SB champions. Points allowed, red-zone defense, 3rd down defense, pass yards per attempt. If we're top 5 in those, we'll be just fine. No matter if we finish outside the top 5 overall or not.