I think we should take a step back and stop thinking of it in terms of video games. First we need to find out what abilities makes a corner great in the nfl. Then we need to think about how these abilities set him apart from other players of his position. After that take what is physically happening in real life and put numbers and game physics to it. I think that will give you more organic looking football were you don't need artificial buffs or penalties to simulate something.
Let's say a corner really excels in those jump ball battles. What is it that makes him better in those situations? You could say let's add +4 to his jump. That would be probably make him better in those situations because he would be able to jump higher. In reality his jumping ability is the same no matter what. He doesn't some how jump higher on those instances. Maybe the real reason he is good in those situations is because he is very good at timing his jump and getting a hand on the ball. The ratings that affect those abilities would only be changed. There would be no need to change the wr ratings either as they would also jump just as high no matter who is covering them. The same for speed. No one is running slower because of who is covering them. There coverage abilities could lead to the reciever not being able to get to their full speed potential but physically there speed has not changed. Madden would then need a mechanic that allowed for the corner to "slow" the reciever when executed. During a single play a reciever could be being slowed down during a play but in an instant gets loose and accelerates to full speed. That's why a -2 on his speed for that play would we inaccurate. It would not allow him to reach his actual speed because the corner had "slowed" him.