Again, I need more information to judge that. For example, you think the machines should have been inspected. Maybe so, but I can think of a plausible scenario in which that wouldn't be correct.
For example, is Fox standing by the defamatory statements and claiming them to be truthful? If they are, then yes, I'd say it's unfair to deny them at least some kind of access to the machines, and that's something that could likely be cured by an appellate court. I wouldn't just write out a $700M+ check without pushing the matter further. I'd appeal the ruling first.
However, if Fox isn't claiming the statements to be true, then Dominion is going to be able to argue pretty solidly that the machines are outside the scope of discovery on the basis of relevance and trade secrets.
I'd have to see Fox's pleadings to make that call.