My take on Brett is that he had a good thing at GB (he was worshipped there actually), and should have stayed there until retirement. I suspect his ego got in the way, not willing to take a lesser role to help the team (even at less pay), take a young QB under his wing, teach/train and keep fresh on the sidelines in case his services were needed.
Is he a leader...hell yes, one of the finest in football history. But, he is more valuable to a team as a back-up. I cannot understand why being a back-up is a bad thing? You get to work your aging body less, and you get to use your mind and experience in a different way. I would gladly take a mentor role, even at less pay, and support the team. I can guarantee his legend would not diminish in a mentoring capacity, as he has already accomplished so much. There have been many other older QBs in history that came off the bench when needed, and helped the team if the main QB gets sidelined.
Now at Minnesota, I suspect he will be accepted just fine. But, like us 40+ year olds all know (myself included), we are not as flexible/pliable/rugged as we used to be. So, I am o-k with the concept of lesser role, lesser pay, less work on the field.