dumervil isn't as effective as some of y'all think. His penalties and run defense are killers...He was super valuable when they had no other means of pass rush, but now with miller they have that pass rush threat. Del Rio only has his guys rush the passer on obvious passing situations and third downs. The Corners have to cover every down, and revis is a more than capable tackler if it ends up being a run.
Chris Harris is the top slot corner in the NFL. Champ and Revis on the two sides and Harris in the slot with Von rushing is a pretty good combination of rush and coverage if you ask me.
Plus, trading dumervil would finance most of revis's contract, so that's not the problem. revis gives you way more for your money than doom.