If the top B12 team is 11-0 (9-0 conference, champ game, and a win over say Tulsa) that won't compare well vs. the other P5s who wouldn't have a better resume. It's setting up a detriment to be invited to the 4 game playoff.
I see what you're saying about BYU not helping though. My thought was that a loss to BYU wouldn't be seen as bad as a G5 loss since ACC, B1G, AND SEC count us as equivalent so harder to make that case.