I mean, if you look at the numbers, MM consistently had one of the better offenses in the league even with guys like Jeff Blake, Aaron Brooks, and Cooper Rush taking significant numbers of snaps.
I get the thought that he was carried to a certain extent by Aaron Rodgers & Brett Favre, but even with lesser guys taking a significant number of snaps, the offense remained top 10-14 (instead of top 5 with). That would still be an incredible upgrade from where the Bears are currently and where they've been historically.