This is one of the major reasons why I have not really been able to get into a franchise type of mode in a game that exposes the true drivers of in-game performance. When true attributes of players are not obscured in any way, then the game is actually tipping what *truly* your best option is (in choosing players, for example), and our best strategy would always be what the in-game ratings tell us, and, probability wise, there really isn't any other options that make more sense.
In that sense, we are being deprived of what would be rather fun opportunities to "evaluate" our players, based on whatever criteria *we* think to be the best. In real life, that guessing game itself is an enjoyable game itself.
If we really truly knew what OVR (or more precisely, their individual attirubtes) all these minor leaguers have in real-life, there would be nothing to enjoy in creating top-prospect rankings, etc. But that's what the game is basically doing, when it exposes their true attribute values.