The problem is you are saying if there was a split of around the top 24 teams would take all the money and time slots and viewership etc. And then comparing those that would be in the 25-75 to the G5 saying they will automatically lose all their fans and viewership.
Sorry we basically have that now, the B1G and SEC get all the promotion and good slots, yet the B12 and ACC still have many games that bring in millions of viewers, and far more than the G5.
If the top 24 teams broke away, the rest will not automatically be reduced to G5, they will end up being in some form of a middle tier, which the only thing that would be different is they would call it as such rather than what they are doing now where they are promoting 2 conferences as being superior in every way, and promoting it far more than the other 2, instead they will do the same only calling it something like P2, SP2, and the G6, etc.
You also seem to not understand that a 24 team league, would not provide enough content to fill up all the sports slots on the major networks, therefore, the so called second tier teams would have to fill those spots, just like the B12 and ACC do now.