Nobody is going to be a big fish in this conference unless they are a dominant team, and at the moment OSU is the only thing close.
Respectfully, some folks in East Lansing might quibble with "at the moment OSU is the only thing close." At worst, MSU is right there with the Buckeyes at the top of the heap.
2010-13
Ohio State: 42-10, 26-7 vs. Big Ten opponents, 1 Big Ten championship, 1 divisional championship, Sugar Bowl win, 1-2 in bowl games
Michigan State: 42-12, 26-8 vs. Big Ten opponents, 2 Big Ten championships, 2 divisional championships, Rose Bowl win, 3-1 in bowl games
Or, using the Big Ten's move to a divisional format/championship game as a guide. ...
2011-13
Ohio State: 30-9, 19-6 vs. Big Ten opponents, 1 Big Ten championship, 1 divisional championship, 0-2 in bowl games
Michigan State: 31-10, 19-7 vs. Big Ten opponents, 1 Big Ten championship, 2 divisional championships, Rose Bowl win, 3-0 in bowl games
I'm not going to bother with Wisconsin's numbers in those time periods, but I would imagine the Badgers (with 3 Rose Bowl appearances) could state a case, too.