I was listening to a taped Monday Night Countdown form the Bills vs. New England game and Ray Lewis was on. He said that Rex's defense is very complicated and that it takes at least 8 to 10 weeks to understand. He said after the players learn the defense is up to the players to "run" it on the field and make adjustments. So the problem "may" of been this,
1. The players were slow to run the system.
2. With the injuries there were players who were confused with the system,
3.There were players who refused to run the system. Or made improper adjustments.
If so with a year to run the system, bringing in players better suited for the system and removing players with systems issues should help the defense.
I HOPE.