I agree with your reading of the GOR. However, the Clemson (and now FSU) argument to me seems to be along the lines of "It depends on what the meaning of the word 'is' is". They are trying to parse the words to mean that the rights are granted to current games for current members and past games for members who left. My limited understanding of contract law is that any ambiguity in contracts is understood to be in the favor of the party who did not write the contract. Clemson and FSU may have some traction if they can show that there is ambiguity. However, the ACC can counter that with evidence of how FSU and Clemson interpreted the contract when they signed it. Which goes to your next point:
With respect to the current/former member argument, the ACC could bring in former FSU trustees to discuss what FSU thought in 2016. They can demand discovery of what FSU trustees were saying internally about the GOR in 2016. The facts are definitely in dispute, and summary judgement is extremely premature in my humble, non-legal opinion. If summary judgement is granted, I don't see how it stands up on appeal. If it does stand up on appeal, I think the ACC would probably appeal to federal court.
I think the ACC should agree to the FSU request to have a retroactive exit from the ACC in August of 2023. They should agree and request summary judgement for that single item. Then they should demand repayment of 2023 and 2024 payments to FSU, and no longer allow FSU to be involved in ACC business. They should demand the exit fee as of August 2023 be payable immediately. They should state the ACC's belief that the GOR still is in force, even though FSU from their own request has left the conference. That is playing hardball, and we would see how serious FSU is about all of this. If the ACC made such an agreement, then this would actually be an item in which no facts are in dispute and the judge could grant summary judgement.
I too am eager to see McKinzie's response to this filing. He stated that he is on vacation in Colorado, but will give his insights soon.