Like Bot said, Deon Sanders was amazing. If every corner could player like him, I'm sure they would.
But even Deon had the benefit of playing in an era in which the rules helped him.
In today's NFL, defenders get flagged for going too low, too high, for hitting a defenseless receiver, making contact after 5 yards, and obviously holding and PI.
After 5 yards, NFL receivers are pretty much running free. Not only are they running free, but they can now run through the middle or wherever else and jump for a ball knowing they can safely catch it without getting blasted.... But if they do, it doesn't matter because it's going to be a penalty and they'll still be moving the ball down field.
Do you really think QB's throwing for an all-time high completion percentage and having all-time highs in QB rating is because DB's are playing too physical or because they aren't playing "the right way"? 10 years ago, a completion percentage of 60 was considered pretty good. Now it's nothing special. In 2002, Matt Hasselbeck finished 5th in the league with a completion percentage of 63.7. Today, that would rank 16th in the NFL. In 2002, PEyton Manning was 5th in the league with a rating of 88.8. Today, that would put him at 18th tied with Alex Smith.
It's the rules making it easy for the offense and hard for the defense. Face it.