Unfortunately, my wife is an Ohio State grad, from a family of Ohio State grads. I've had to watch those @#$% play for years, which made our struggles on the gridiron even more difficult to swallow. But I digress--that program is humming on all cylinders right now. Michigan isn't anywhere close to it.
Also, the college game is different than the NFL game. College coaches are successful for some different off-the-field reasons [i.e., recruiting] than what it takes to be successful in the NFL.
Harbaugh is an NFL guy. My opinion only, but he is only at his alma mater temporarily, and will jump ship at the earliest convenient opportunity when a good NFL gig comes along.
Let's just say for arguments sake that he's at Michigan for three years--a fairly substantial commitment for a guy who's intention is to get back to the pros. Well, one of those seasons is already in the rear view mirror. That means he'll have two years to make a mark at the collegiate level. No matter what success he achieves, he won't put in the amount of time Meyer has, nor will he probably [again, my opinion only] be around long enough to realize the fruits of his labor, and for those recruits to actualize their potential.