What I think McShay is saying there is basically that there is a lack of CBs who are obvious top-15 picks. That's true for a couple of reasons, the main one being Marcus Peters' draft stock falling after he was kicked off his college team.
What I don't think McShay is really referring to--or where I disagree with him, if I'm reading the statement wrong--is that I think there are a lot of good corners in this draft who have potential to be really good. With the possible exception of Trae Waynes after the combine he had, there's no 'can't miss' prospect... but then again, there very rarely is. Even the guys who eventually live up to the hype, like Haden and Peterson, rarely get anywhere close to it as a rookie. Then you have the other 'can't miss' top of the class prospects like Morris Claiborne and Dee Milliner. And I think Justin Gilbert's going to join that group too, because being the #8 pick aside, I'm not very high on him.
I don't believe the hype on corners when it speaks well of them, and I don't believe it in years like this one either. For a number of reasons, the main one being that no college corner is anywhere close to being a finished product, even relative to other positions. And since the 'can't miss' guy seems to be whatever corner played for a major conference team, came in 6'0" in the combine, and ran a sub-4.40 40, I'm inherently skeptical of any corner who gets that kind of billing. Half the time, they're being awarded that based on a deeply flawed criteria that doesn't speak to what they'll be doing in the pros. If I see a long corner who can consistently press at the LOS, can flip his hips smoothly and can get in and out of breaks quickly, I see a future outside starter. I don't care if he 'only' runs a 4.5 at the combine, as long as he isn't getting beaten on tape. That's why I like Peters so much, and why I was borderline happy that he ran the 40 that he did. If he runs a 40 time that's consistent with his game speed, he's probably a top-15 pick right now even with the character concerns. Since he didn't, there's a shot that he falls to us.
Basically, in general I think that worthy day-one starters at CB are extremely rare, so I don't see why the lack of one in this class would be a big deal. If everyone agrees that there isn't a day-one starter right now, then for once they're talking sensibly, because even the best CBs need time to develop. Best case scenario, you get guys who flash a lot of talent early but are inconsistent and have holes in their game. If you get Jason Verrett or Kyle Fuller, that's pretty much a win since it's unreasonable to expect more than that from a rookie corner.
So if we're looking at ceiling instead of plug and play potential, I'll go out on a limb and say that I think Marcus Peters is the best CB prospect of the past two years in terms of his on-the-field potential. He does have some obvious character concerns, considering that he got kicked off his college team, but FWIW Steve Sarkisian has been going to bat for him. And there's a cluster of guys following him who I don't think are as talented, but who could all become plus starters with proper coaching. But they absolutely do need coaching.
As far as what that means for the Pats - it means in 2015 our corners are probably going to be a weakness. Kinda sucks, but oh well, it is what it is. If they go and draft corners now, the impact should be felt this year--especially if they bite the bullet and take Peters, who can at least play right away IMO--but it should be more felt in 2016-2018.