In his stint with the Bears, his biggest problem was poor decision-making. He wasn't ready for the NFL. He scrambled around and then threw interceptions. McMahon scrambled around - and threw touchdowns.
After seasoning in Canada, when Flutie returned to the NFL he was a much better, smarter, savvier and more mature athlete. He was a pleasure to watch when he played for the Bills.
This might interest you from the Bears History Channel:
It has been well documented in several books on the subject that the off-field distractions played a part in the demise of a potential dynasty. Players envied others that received more attention (and money); even player's wives became competitive with each other. In a 2004 documentary, then General Manager Jerry Vainisi said he was very concerned about the team focusing too much on off-the-field issues, but with the Head Coach doing more endorsements than anyone, there wasn't much that could be done. In the same documentary, Ditka said "if you think I wasn't going to enjoy the fruits of my labor, you're crazy."
Then there was the trade for quarterback Doug Flutie, the mother of all distractions. Ditka and Vanisi engineered the trade for the diminutive signal-caller, reportedly against the advice of President Michael McCaskey and personnel boss Bill Tobin. Ditka and Vainisi felt they had to shore up the quarterback situation with McMahon's recurring injuries, so they traded '87 draft picks for the 1984 Heisman Trophy winner from Boston College.
The trade for Flutie did nothing but inflame the team, which felt to a man that Tomczak and Steve Fuller were capable of carrying the Bears to another Super Bowl.
http://www.bearshistory.com/seasons/1986chicagobears.aspx
I am not a football fan, but when Doug played for Buffalo, he just brought that team together and provided enthusiasm and excitement that I hadn't seen before or since. He was a leader who brought the team together.