This is how I always viewed potential. Your natural gifts, the physical limits of what your body can do, are your potential. I'm fine with having caps on that in Madden cause there's caps on that in real life. No matter how hard I or almost any other human being on the planet practices, we're never going to have the physical gifts of a Michael Jordan or Barry Sanders. That's just genetics.
But those gifts only determine your potential. You still have to meld those genetic talents with mental discipline and knowledge. That's what makes guys like Jordan and Barry so rare. There's been and still are guys that have as much potential as them, but it almost never happens that they're able to put it all together like the legends did. You hear it all the time on draft day: "This guy is raw, but he's got all the physical tools" or "If this kid can catch up to the speed of the pro game, he'll be a great one."
So it's not a problem that there's a potential rating in Madden. The problem is that there aren't as many factors affecting a player fulfilling that potential in Madden as there are in real life. In Madden, we have on the field production and injuries determining if a guy can live up to his potential. In real life, we have both of those but also have off the field issues, character being the biggest one. How many guys have slid down draft boards even though they were physical freaks because of character issues? This is huge when determining whether to take a guy because so many players with good potential just can't keep their noses clean.
So I don't see a potential rating in Madden as being any different than real life. You scout a guy enough in the real world, you'll know what his physical ceiling will be. You then just have to hope he can learn the mental part of the game, stay healthy, and stay out of trouble. I guess 2 out of 3 of those factors for Madden ain't bad.