In Claiborne's case, I simply think he lacks at least football intelligence. Perhaps he has trouble grasping the concepts he's being taught...or translating them to the field? In college, Claiborne could get by on his athletic ability, and despite playing in the SEC, he often wasn't facing NFL caliber QB's. He also seems timid at times, and confidence could be a factor as well. He seemingly went out of his way in camp to show he was indeed tough enough with the jawing, etc.
Carr sometimes seems overmatched athletically. Applying to this season...his Mother's passing could certainly be weighing on him as well. But he struggled mightily at times last year as well.
Both Marinelli & Henderson have coached some very good DB's...who grasped & played well in their respective defensive schemes. Even guys like Major Wright, who wasn't resigned by the Bears, played fairly well with Marinelli as DC...and in 2012, the Bears starting CB's, nickel back & safeties, had a combined 21 Int's. I would think that they're teaching the same things...only to different players. I was hoping the Boys would sign Charles Tillman this offseason despite his age...simply to hopefully help with grasping the defense, communication, showing younger guys how to study film, etc.
As of now, Scandrick is their best guy in coverage...and Church is usually pretty solid in run support/tackling. But they seemingly simply lack much talent at any DB spot.