IMO, the biggest thing holding us back is the defense. Our offense was fine last year, we averaged 33 points/game (roughly the same as the last 5 or so years). Run the ball, pass the ball, whatever.
But the defense needs to drastically improve before we can even start thinking about winning a B1G title.
Against BYU, Illinois, and Wisconsin the D had chances to put the game away in the final minute, but couldn't get a stop. Against NW, we needed a stop in the final 4 minutes to get the ball back down 2, but couldn't get it.
Looking at last year, we need to be much better against the pass, both in coverage and finding a pass rush.