Guess I will throw my 2 cents in this circus of a debate. My impression of this is that from what RR and Hurney stated is that McClain basically quit. That is to say that I think he became complacent about his job and didn't care to get better. It happens with athletes at all levels.
Sometimes a person goes all out to get to the next level and when they get there they stop trying. They feel they have arrived and can rest on their accomplishments so far. In the NFL we all know that's not the case. Scouts and Coaches cannot predict that accurately, nor can any of us. All they can see is what the person has done so far before the draft. In this case they saw enough to draft him. After that it's on the player to take on a new challenge to be better at his craft and stave off all challengers to your position. It appears McClain wasn't listening when he was told he needed to improve.
The FO gave him a shot to succeed because thought he had it in him to be a quality player. He just wasn't living up what was required of him in their eyes to be the player they needed.
Just that simple really.