I think your wrong about the progression and regression rate. I think it's decidedly tilted towards progression. I think generally speaking, the guys drafted and signed improve their skills as time goes on. The guys at most positions seemed to be fairly well coached by their position coaches.
Let's take a look at the Packers draft picks since the new CBA and rules for offseason practices were introduced six years ago.
Here's a list of players I believe significantly progressed during their rookie deals:
2011: Cobb, House and Guy (although with another team)
2012: Perry, Hayward, Daniels
2013: Bakhtiari, Tretter, Hyde and Johnson (with another team)
2014: Clinton-Dix, Adams, Linsley
2015: Montgomery, Ryan, Ripkowski
That's a total of 16 players out of 46 picks, for a rate of 34.8%. Even by removing Sherrod and Franklin from the list it seems it is decidedly tilted towards regression.