Do we really have questions at every level though? I think CB is the only question mark. Sure we could use a DE upgrade, but wouldn't call that position a question mark as I'm assuming either Ben or Kemoko will be good enough, with Buck making their job a lot easier.
It keeps the #1 receiver from beating the CB deep, not necessarily shutting him down. If the CB is unable to be physical, reactive, or athletic, then he gets beat regardless. And being matched up against the #1 WR is more of a man-coverage thing since the CB might release the WR in zone coverage.
Ed Reed has value when you have a Vontae Davis type of CB on your defense, and that type of FS doesn't have much value if you don't....or don't plan to, JMO. And the Vontae Davis types are typically harder to find worth more to a defense than the FS (because the CB has to shut down more plays than just the deep ball, including supporting the run like VD used to), unless maybe you're the one off exception like Ed Reed in his prime.