Waggner has a safty's mentality and a CB's body. McNeil is young but shows a lot of promise (only DB that shows proper tackling just isn't strong enough yet), Coleman is a middle of the road CB with what he's shown so far, Moore wants to make the big play so badly that he usually ends up blowing coverage or missing a tackle, and Gordon is a nickleback that can tackle well and is decent at coverage.
The overall reason they're looking so poorly? The scheme. We constantly drop one safety deep and leave the corners by themselves on the outside in one on one coverage. Sal needs to stop looking at this defense as 11 individual players and start looking at it as 1 defense composed of 11 players.