What Favre is is a sandlot superstar. He relies on his arm and his instincts to make things happen. Sometimes he gets good results, other times no so good. He has to have a lot of talent around him and that talent has to have the capacity to freelance on the same wavelength as the QB. He doesn't want them worrying about system because the more they think the less instinctivly they play. And still games remain a relative crap shoot his way, particularly against better coached or more talent defenses who have a pretty good book on what his way entails and the pitfalls to watch for.
The NFL is a coaches league with a salary cap where you have to make due with what you can afford. That is accomplished via system. Install and teach a good one and even marginal talent can help you win with reasonable consistency. Add better talent to that system and you win with more consistency.
Mangini and Shotsie, Jr. might as well watch JETS games from a luxury booth going forward. Brett ain't following no damned gameplan, his gameplan is do what I do and give us a chance. Details like personnel packages, formations, scheme mean nada to him. He did it the system way in GB 2007 to placate that HC and GM, and while it worked to an extent it didn't win him another ring and it exhausted him mentally in the process. It means nothing to him that adhering to a system built a foundation that is now paying dividends in GB in his absence...as far as he's concerned they should have shut down Lambeau once he retired and he only came back to underscore their foolishness. The fact that GB seems to be not only surviving but thriving has forced him to take the laughable stand that the backup obviously learned a lot just watching him...
If your system is not about accommodating Brett Favre he's not interested in it.