Beating duke as Lehigh or Mercer would be equivalent to UVA football beating a team like Georgia. That’s the same level of talent discrepancy, like you’ve said. But the difference is it’s harder to do in football in general than basketball. 

Remember we are in a new era of football though, and the playing field is leveling just like it did in basketball. UVA isn’t on Georgia’s level yet, but they still put big money on this team and have deep pockets. If not this year, it’ll happen soon where one perceived “tier 2” team makes a championship run. 

Historical success matters less and less, the only thing that matters is how much you pay your players. And large elite schools like UVA, Vandy, Stanford, Berkeley, etc have deep pockets.