It's mainly that they need to rework how awareness works. Right now, awareness is pretty much the equivalent of how much the CPU cheats by already knowing where you're throwing the ball before the QB even runs the animation of whatever button you hit. The higher the awareness of the overall defense, the tougher it is to play against that defense, no matter how bad they are in other categories. I've been meaning to do some tests to see how low speed, agility, and acceleration could be before awareness doesn't make up for it anymore (in fact, I might do this when I get home) but I'd venture to guess that speed, agility, and acceleration could be much lower than people would be used to without it affecting the ability of the defense at all.