I tried to tease this out using regression a couple years ago to get solid ideas of which teams impacted the viewership more than others.
It was really hard.
In addition to controlling for the channel, and the timeslot, and the team 'brand' - you also have the teams ranking, the opponents ranking. Getting all the data, even proxies for the data, wasn't really feasible for an amateur.
But my takeaway was VERY ROUGHLY, the channel/timeslot drove probably 60% of the ratings, and the teams involved (all mixed up as brand, rating, opponent) was 40%.
So ABC at 2:30 game, a mid ISU vs mid opponent would get say 3M viewers. But a top 10 matchup with Ohio St would prob get more like 5M. Again these are back of napkin type numbers.
Alternately, the same matchups on ESPN+ might be 600k and 1M.