Well, I know USC beat the Big Ten champs 4 times since 2003...
PAC 12 won six bowl games this year alone. I looked for a comparable stat, but couldn't find one easily. The Big Ten one came from an article today.
I don't think there's much debate that the Big Ten has been a disappointment in big games, is there?
You did say "January bowl games", though.
I went through the conferences bowl records team-by-team for the past 4 years, and other than Stanford and Oregon, there hasn't been much for January bowls. Even Oregon has been somewhat mixed. Plus right before that 4 year time, they lost the Rose Bowl to Ohio St.
There's no doubt the Big 10 has not been up to earlier standards, and has weakened over the last several years. The question is by how much. This year I was also one who lamented how weak they were, but the post-season performance has been much better than advertised, certainly not down to the level of derision the conference has been suffering.