Tennessee and Georgia were both ranked in the top 10 when we played them. we actually beat Tennessee twice as a top 10 team. Sagarin rankings? Gtfo here with that joke of a data set.
You won't find any metrics in 2004 that indicate Auburn had a tougher schedule than USC.
Back to the point: Auburn didn't win the national title. And Auburn also never claimed a title in 2004. If you feel differently, you should go to the athletics office and complain about the banners that aren't on display.