re: Has any college football program fallen harder than Southern Miss?

Nebraska.

Southern Miss was generally a competitive team for a good many decades of their history, but Nebraska was a national power. The hold the NCAA record for most consecutive bowl appearances and, for a good portion of that run, bowl games were few and far between. You had to be worth a shite to make one. We're talking about a team that went from finishing in the Top 10-15 every year to not making a post-season bowl game since 2016.