All of this, one player will not make a difference, is nonsense. Since the trade, Mr. McFarland has made a huge conribution to the Colts' Super Bowl run.
I have not looked at the run defense statistics, but they have got to to better than what they
used to before 92 got here. He, alone, has been disruptive in the middle and it looks like our LBs(even Gilber Gardener) are free to make plays. Rob Morris has looked probowlesque in the past couple of games. It seems like whoever makes the tackle(for us), is confident that he's not going to see a OL(to tackle), but a RB. And that is boosting our LBs confidence(and ability to make plays behind the line of scrimige.)
In conclusion, the return of 21 will make a significant difference, but the biggest difference in our defense we've already witnessed.