The G--men were putting some serious Ds on the field during those years and their battles with the 9ers all time classics.
Ironically, back in the 80s the Giants' secondary was always their weakest area -- typically, they would have one Pro Bowl level player (Haynes, then Collins) and one other solid player (Terry Kinard, for example) at the same time. The other two (Perry Williams and Kenny Hill, for the most part) were solid tacklers who fit into their system well, but were marginal by themselves.
For a solid defensive backfield from that era, look no further than the Kansas City Chiefs. The late-80s backfield of cornerbacks Albert Lewis and Kevin Ross, strong safety Lloyd Burruss, and free safety Deron Cherry, was undoubtedly one of the best of all time. The Cleveland Browns of that era also had a great backfield -- Hanford Dixon and Frank Minnifield at the corners, and Felix Wright and Al Gross at safety.