It was more of a general statement about all young QB's, not just JP. Because of the Pittsburgh situation, all rookies are going to get ripped apart if they don't win immediately. Replace the word "rookie" with "young" and my point still stands.
As for your Favre comparison, did he miss a lot of reps due to a broken leg? Just because one player who became a star after sitting out his first season and then put up decent numbers in his second season doesn't mean that the same applies to every single QB out there. There are different factors in play from team to team, player to player.