Miami Dolphins defense keeps core players, but is unit any better?

This fundamental truth first: The offseason is the time of year when NFL teams are trying to improve. If the seeds of that improvement reveal themselves in 16 bursting blossoms during the regular season, then it is in the offseason when that harvest was sown.

So this is the planting season.

And this planting season the Miami Dolphins wanted to grow a crop of good defense because last year their defense -- not very good when everybody was healthy early in the year -- was downright bad at the end of the season and into the playoffs after it was ravaged by injuries.

Thus the Dolphins defense finished ranked 29th in the NFL. (This is a stat the NFL goes by that measures a unit based on yards…