If the ACC is completely unwilling to settle on anything then the league and ESPN will be in court for several years, with many things made public that they probably would rather not be. Then FSU will leave anyways. The reason the Big 12 gave up $60 million dollars and let Texas and Oklahoma off the hook:
As others have said, the time remaining on the GOR contract is a very big difference.
Combined with that, the other difference I haven't seen mentioned much is the "rock and a hard place" position that FSU's actions have put the ACC in.
I agree with your assertion that ESPN and the league may be in court for several years, with many things
potentially coming to light that they don't want. So the ACC has two choices:
1: Let FSU buy their way out for a lower negotiated fee, including both the exit fee and buying back their media rights. This approach saves the ACC and ESPN from thing they don't want public getting out - but also almost certainly opens the door for other teams to follow FSU's playbook and make the move to other conferences. In the things that have happened in conference realignment in recent years, it is almost certain that other teams would leave, and other conferences would embrace the opportunity to go "shopping."
In this case, in the best case the ACC's media deal with ESPN could collapse due to the lack of teams with enough pull to draw eyeballs; in the worst case, that happens, the conference can't find a buyer to offer a sustainable media rights deal, and many teams find themselves in a Pac-2 situation. Either way, the ACC's survival seems quite threatened.
2: Dig in and argue the whole thing, knowing that the alternative is a "run on the conference," so to speak. In this case, the ACC accepts that some dirty laundry may be aired. But with the alternative being almost certain implosion of the conference, it's a no-brainer. You can't protect the conference from dirty laundry if there's no conference to protect.
This is why I don't see the ACC settling for a substantial discount on anything, just to "keep some things quiet." Unless it's information that would threaten the existence of the conference, letting that info get aired out can't hold a candle to the other choice - from which the conference's destruction is almost a foregone conclusion.
That's why the Grant of Rights was created in the first place (at least according to the way I and FSU's former Board of Trustees see it). It seems to be doing its job admirably.
FSU may have some merit to their case. I personally don't think so, as they made an agreement and accepted substantial benefit from that agreement. But whether they do or don't, this is a fight for survival for the ACC. If this was happening in 2032, I think the ACC's approach would be completely different, and more willing to work things out. But not now, with what's on the line.
NB: Not a lawyer. Just a dude trying to keep my own biases in check and look at the parties' tactics, incentives, and motivations objectively.