Well actually two one-loss P12 teams have already made the playoffs, so clearly we can get a mulligan. In 2019 we were a shoe-in despite losing to a mediocre Auburn team until our late season loss to ASU knocked us out. This season we probably get in if we beat Utah twice, despite losing to Stanford. Of course beating a highly ranked USC team would help the resume, but beating any highly ranked conference team would do the same.
USC has the tradition and the huge TV market that makes them very attractive to the media, but that really doesn't do much for the rest of the conference. The chances of a one-loss P12 champion getting into the CFP are still very good with or without a dominant USC. My point is that it hasn't been the weakness of USC that's kept us out of the CFP, it's that we are losing critical games in November.