You're obviously a sensible football fan who happens to also play video games. It seems like most of the people who post on this board no little about the actual game of football or just aren't sensible. It is a common perception among NFL coaches, GMS and analyst that some players and some positions progress better by not playing rather than getting thrown to the wolves. The QB position is the most notable. Many times a team will not start or even play their big name QB his first year out of fear he will be ruined by playing too early. Carson Palmer is a classic example of a player who was held out his first year and had immediate success. THen you have Matt Lienart and Vince Young who were thrown to the wolves from day one. That experience has probably ruined their careers.
The other negative with performance based ratings is you have to remember that YOU are controlling the players. If you are good at running all the runningbacks you control will likely improve rapidly.
And you don't need performance based progression. It's quite possible that an 80 OVR rated player who wins the MVP is a player that just plays beyond his capability or ratings. Besides, the overall ratings in Madden means little anyway. The most important ratings are the attributes specific to each position. A 75 OVR WR with 90 catch ratings, 90 RTE ratings but 60 AWR could be much better than the 85 OVR rated WR with 80 catch ratings, 80 RTE and 95 AWR.
I like the potential rating with a little modification. What I think they should do is still give out the ratings but just don't make it an automatic that a player with A potential will improve to a 90+ player or a player with B potential can never become a 98. The way it should done is to have the player with A potential have a better chance of improving to 90+ and a B a lesser chance, etc. For instance, an A potential player has a 80% chance of improving to 95+, B potential a 70% chance, and so on until you get to say an F potential guy who maybe only has a 5 or 10% chance of getting to a 95+. On the flip side, an A potential player could have an 20% chance of never reaching his full potential of 95+ and may never improve much if at all past his rookie ratings. This is the best way to have gems and busts. Even real NFL scouts never know the real potential of a real player or whether that player can reach his full potential. My idea would better simulate that.
The problem with my idea above is video game freaks can't see past their linear line of thinking. It's either black or white for most. If they draft an A potential player that only improves from a 75 rating to a 80 rating they will cry foul that the potential rating is broken. Hopefully EA has more common sense than that.