He still did a GREAT Job for not having OC experience. You want to see a horrible OC destroy a QB early, check out John Hufangel and how he impacted Eli. Eli did A LOT better once Huffy was fired.
I also think the league has caught up in some ways with some of JG's concepts. However, the output from his offense is pretty impressive. Miles, Witten, and Romo have done well under JG. I know Witten is personally tight with the Garrett family especially old man Garrett. He spoke at the coaching clinic camp I was at. These are the type of connections that help. Witten has hall of fame talent, but it helps to be tight with the family like Garrett's who have their hands on the team.