This is absolutely a classic anti-trust case. The major conferences, by themselves, are an anti-trust violation. The conferences market power is solely based on the collusion of the individual members. The universities are separate legal entities, so there is no free pass to collude with each other in a conference for greater market power. Since illegal collusion is the basis for the SEC's and Big 10's, and Big 12's and ACC's for that matter, market power, the problem does not improve at the conference level.
Market concentration is another test for anti-trust. It is a complicated formula for market concentration, but the Justice Department generally frowns upon mergers that will consolidate more than 20% of a market into a single player. The 4 major conferences have a stranglehold of about 80-90% of the total revenue available to college athletics. Maybe there is still some competition between them, but the existence of a CFP playoff model where the 4 major conferences all have a permanent automatic bid to the CFP, which they got because of their prior collusion into conferences that had exceptional market power, is a really big problem for them legally.
Finally, the fact that their prior collusion is enabling the early conference members to drive grossly unequal economic terms to new members is even a bigger problem, because it proves that there is market power from the collusion, and that the conferences are using their collusion to drive unequal terms. Ironically, ESPN, with its pro rata per team structure in its contracts, actually lets itself off the hook a little here because it is not directing the unequal revenue splits internally at the conference. Fox and CBS are probably in the clear too. All three are still exposed on the monopolistic ripping up of the Pac 12, since they all appeared to play a significant role in that.
I do not think there is a chance the conferences would survive an anti-trust lawsuit. The fact pattern is terrible, and sports leagues usually lose anti-trust cases to begin with, so the hurdle is not that high. I suspect that the P4 know this, which is why they are so generous with the G5 conferences in the CFP splits. The G5 has a lot of leverage in the revenue split negotiations after what just happened with the P5 going to P4.