I wonder if we're not watching something a little more fundamental. Big CB Slot/FS being added from former CBs. Maybe part of the problem was Meriweather and Sanders no longer had a role on this particular defense.
IMO, Butler is a capable CB with confidence issues ............. he is not, however, a Slot CB/ FS capable player. It explains drafting Dowling, when we already had four CBs (Butler, Arrington, Bodden and McCourty). Somebody posted, somewhere earlier, that the small CB is no longer a NE player. That may be correct.
Butler can play football still, hopefully, we get something for him.
OTOH, I could be wrong but it seems to add up. Unless Meriweather was a locker room/Discipline problem he is a better FS than what we presently have. ...... So, maybe FS as a position changes on this team.