This particular season's tournament results don't make the Big 12 a bad conference. Upsets happen. I don't think it means the league should have been only a 4 bid league or something.
However, only 1 national title and no one besides KU making Final Fours (WVU was Big East) for 10 years is a bad look for the league and the quality of the league. Until someone else makes a run, it will continue to look bad.