Eagles were ranked 29th in defense due to the large amount of yards given up. However, when you consider that they had the most defensive snaps in the league, that shouldn't be surprising. If you look at yards given up per play, they were 12th in the league.... that's pretty darn good.
They were also 5th in take aways and 17th in points (with only two real blowouts in the Denver game and Minnesota game).
The Eagles defense is not nearly as bad as people think and if they can generate a consistent pass rush, they will be a force.