Right now, on every single play at least one defensive player doesn't do his job. He forgets his assignment, overplays, or tries to do someone elses job. There is no trust. Has little to do with schemes. If you make the scheme more complicated, a la the Jets, it just more likely for there to a be a breakdown. If you make it too simple, then it will get figured out by the end of the game.

 

The only way to really fix the defense is to get them off the field. Limit their number of plays on the field, so that other teams have less time to work their weaknesses and expose them.  That and maybe one in while, going all in with an All Out Blitz all because if there will be a blown coverage anyway, might as well have that guy blitzing from the start. 

---