The fact that he progressed (no, he did not regress) is not debatable. It is there on tape for all to see in numerous examples, and there are resources to get copies of those games for any who don't have them. Not eveything in football is subject to opinion even though we feel empowered with all of our varying opinions of many aspects of the game.
What IS debatable , is whether or not JP will ever become a complete and successful NFL QB. Sam Wyche, IMO, had a very good relationship with JP and helped him out a great deal.