I agree with your premise.I agree with the spirit of what you are saying, but I want to throw out one nitpick. Average viewers can be a little deceiving over a short timeframe. For example, Indiana had very good TV ratings in 2020 because they were surprisingly good, and they played Michigan, Ohio State and Penn State, didn't play any cupcakes and played on ABC or FOX for HALF of their games. Fast forward to 2022, and their ratings (even with Michigan, OSU and PSU on the schedule) kind of sucked because they played on BTN and FS1 a lot more. Of course, the teams with the most viewers are theoretically on the big-time channels BECAUSE they deliver ratings and don't get the ratings as a favor from that broadcast slot, but Illinois drew very good ratings whenever we got the chance to play on a big-time channel like ABC or FOX or ESPN. Conversely, Penn State did not draw much better than us for their games on BTN.
What I am trying to say is that "average viewers" over a short timespan will correctly capture that Michigan and Alabama are ratings darlings, and it will likely capture that not a lot of people tune in to watch Northwestern or Vanderbilt, regardless. However, schools like Illinois, Wisconsin, Michigan State, etc. will be at the mercy of when they're playing. Our ratings were MUCH better last year than the year before, and it's because we got some great opportunities to play on national TV. FOX, ABC and CBS get great ratings almost no matter what ... sure, it's way better when it's OSU/Michigan, but we already knew that. You cannot watch Illinois play Purdue on BTN and watch Wisconsin play Purdue on FOX and assume Wisconsin has more fans based on those ratings, for example.
Here's to hoping the Illini get plenty of chances to be seen by a national audience this year! The chance to play PSU on FOX for Big Noon Kickoff is massive, and getting a night game audience on NBC for Purdue is great, as well. Not sure how ESPN2 would draw on a Friday night for the Kansas game, but maybe better than we think.
But there are somewhere in the range of 15-20 teams that have built up brand equity over decades, which I just do not think will dissipate quickly. I feel that these schools will almost always draw viewers on whichever channel they are broadcast. The SEC and B1G now have most of them: Alabama, Auburn, Florida, Georgia, LSU, Oklahoma, Tennessee, Texas, Michigan, tOSU, Penn St., Nebraska, USC, Wisky, . . . and then Notre Dame, Clemson, and maybe Florida State, Miami and TAMU.
There is another roughly two dozen additional teams whose games can draw big numbers (a) in years that they are competitive, and (b) when shown on an over-the-air network. I think this group includes pretty much every SEC and B1G team not named Indiana, Rutgers, Northwestern, Vandy, Kentucky and Miznoz.