I remember being surprised the Pats passed on adding a cornerback for much of the draft this year, but it seems clear now that they liked a lot of the late-round / UDFA options. If someone had snagged Roberts before they picked in the 7th, they probably would have taken Coleman or Hill or someone.
The draft was considered weak for CBs, but there are quite a few contributing as rookies: pretty much all the first-rounders, second-rounders Eric Rowe in Philly and Ronald Darby in Buffalo, and even late-round / UDFAs like Bryce Callahan in Chicago and Quandre Diggs in Detroit. At the risk of going off on a tangent, it seems like teams are willing to "pay" for height and 40 time and the guys who are sub-6'0" with 4.5-something 40-times can be pretty good values.