You are missing the root measure. It does not matter if they are normalizing the numbers. The numbers are ordinal. It's the scale. The. Scale. Is. Ordinal.
1. People are now freaking out about a 45 FV vs a 40 FV
2. It's still ordinal so it's someone's opinion.
Here is the thing. Those people who are doing the rankings are normally very good at what they are doing or else they would not be doing it. But it's based on their judgment, which is better than mine or most people outside of baseball. But then taking a judgment and hocus pocusing the judgments into numbers doesn't not magically make them better than what they are. It's an organizational system for ranking prospects according to performance and projectability. But, it's often wrong and there are inherent problems associated with distilling attributes into a ratio-type measure.
BTW> The 20-80 scale was started by Branch Rickey. They took that scale and made standard deviations based on each 10 points.
Edit: Also, it's a no no in science to use standard deviations with ordinal data.