The reason I brought up Foles is because Wentz WAS on his rookie deal, and Wentz was on his way to winning an MVP before he got injured. It was Wentz that put the Eagles in the position they were in. If you remember, Foles was pathetic in those two starts at the end of the season and then played great in playoffs.... but if Foles had been the starter the entire season, there is no way the Iggles win.
As far as Mahomes, we all know that Mahomes was and is simply an incredible QB. Being on his first deal had nothing to do with winning a SB in his case IMO.