To demonstrate what
@DVontel is talking about, I will use a player that we are all familiar with: Calvin Pace.
The Cardinals drafted him and tried to make him work as a 4-3 DE for years and he sucked!! He was awful, never really amounted even a lick of pass rush at all.
Was this because Pace was a trash player? No. Pace took off once he was moved to 3-4 OLB and actually looked like a good 1st round pick.
He was never a reach and was always a good player, but he wasn't worth a high first round pick because he was a scheme dependent player. Some of the corners available after the first 3 will be like that, scheme dependent players.
Patrick Peterson is a scheme dependent player...he's always been meh in zone coverages, and excels in press man. That's why resigning him was always in question because Vance likes to run zone coverage a lot more.
There are still probably a half dozen vet corners out there that will be able to at least replicate what the Cardinals got from Peterson and Kirkpatrick last season. Maybe more than a half dozen.