I get what you are saying, as that has been the conventional line of thought the past couple years, myself included. I'm just finding it hard to believe the offense can be any better next year by removing the best deep threat the team had.
If Zimmer's goal is still to have a world class defense providing the offense a low scoring threshold to reach, he is at least a couple years too late. It's hard to say what happens with Joseph gone, but it's a given that the CBs will be less experienced. I'm hopeful that the Hughes and Hill provide improved play, but both are big question marks right now. Therefore relying on the defense to keep the game in the 20s is not a good bet. Consequently, trading away a highly desirable talent on already shaky offense doesn't make much sense to me.
Maybe they will kill it at the draft and I'll be back on the bandwagon.