Yeah, and the funny thing is that your math example is predicated SOLELY on "same TV rights, just divided among more members". And, sure, technically that is true IF IF IF the TV deal doesn't get renegotiated.
But the other revenues would go up as well. The advertising the Big 10 does, the merch, the licensing...it really goes up once they have access to CA and L.A. itself. This always happens big with merch on a "switch". UM switches to adidas - bump. UM switches back to Nike - bump. But the interesting thing with everything else (ads, licensing, etc.) is that it becomes a permanent bump. And I definitely think that USC/UCLA bring an out-sized impact, even moreso than simply adding 2 teams, they are essentially opening up access to the entire west coast.
Also, during the earlier Big 12 problems (when Nebraska/Mizzou left), I kept telling people that the network "paying the same amount for fewer teams" was going to be the death of the Big 12. Because they got "more money" per school back then, they got used to it. But it was artificial. It was NEVER going to be that good again, and I think Texas and OU figured that out. So before they had to be humbled into taking less money on the next deal, they just jumped to the SEC.
Here's the reality. If taking Notre Dame and a couple of other teams will NOT put the ACC into the same numerical category as the SEC and Big 10, then it's just half-measures. Not good enough. Bound to end in eventual failure.
So who's left in the game? Disney/ABC/ESPN is all in. Fox is so-so. CBS didn't push hard enough to keep the SEC package. NBC has pretty much run up the white flag by shuttering its cable sports channel. So, yeah, in light of all of THAT, I'm not sure that Disney/ABC/ESPN bake enough pies to keep everyone (financially) happy.
There's just not enough room on the dial, and not enough money to share, for five Power Five conferences.
Get busy living or get busy dying.