If you don't give any weight to playing better late, but instead look at the entire year, OU had a better year. Ou had a better record against stiffer competition. OSU won 2 of 3 head to head, would be their best argument.
Fact is that OU got in ahead of OSU and ASU got in ahead of USC, for the same reason. In both cases, the records were similar and the committee just put the team that didn't buy their players in over the schools that did.
USC and OSU couldn't be directly or openly punished because the proper process hadn't been followed, but they both had assistant coaches ARRESTED BY THE FBI for buying or trying to buy players. Enough smoke that the committee just decided between fairly equal teams to give the benefit of the doubt to the teams that weren't involved in the scandal.