The media likes to talk about Claiborne, but I think a big key to whether or not the Cowboys are deep in the secondary will revolve around Corey White. He showed some really good ability with the Saints but lacked consistency. If he can become consistent, I think it really improves the depth at DB. Marinelli is much more about teaching fundamentals and having a more simple scheme then Rob Ryan, so I think that will be good for a player like White.
Wilcox made some mistakes last year no doubt, but when I went back and really studied him on the All-22, about half of what I originally thought were mistakes by him were actually mistakes by the players around him. Marinelli requires the FS to play the scheme and assume that the surrounding players will do what they are expected to do within the scheme. When LBs or CBs don't play the scheme correctly, it makes the FS appear to have been out of position. Bruce Carter was one of the culprits. Cam Lawrence and Keith Smith played a few snaps at LB and they screwed Wilcox over on most of those snaps. RoMc was not perfect in this area either. The CB Moore had a tendency to freelance at times. Claiborne when he was starting early in the season made a few really dumb decisions.
I lot of playing within the scheme is fairly simple stuff. If the FS expects the LB to funnel the runner inside but the LB lets him get outside, then the FS is out of position. Those types of issues are often not really visible on the broadcast footage.