"But what how does that relate to a Big Ten opponent? Chattanooga is better than SIU-Carbondale, and the Salukis just beat Northwestern, so is Chattanooga maybe better than the bottom-of-the-barrel Big Ten teams? Maybe we should say that the 9th-best FCS school is as good as... the 100th-best FBS school? Or is that maybe exaggerating things too much?"
If you trust it, the Sagarin Ratings attempt to combine FCS & FBS. They have Chattanooga as #9 in FCS, #115 overall (would be #106 in FBS). The comparable FBS teams to UTC are NIU, New Mexico, Old Dominion, Georgia Tech, South Florida, Nevada, Ohio, La Tech. https://sagarin.usatoday.com/2022-2/college-football-team-ratings-2022/