What case law.
Actually, I think you misheard or the lawyer misspoke. I don't think there is any "case law" on congested airspace. What is true with regulations in general is that if the regulation needs interpretation, the ALJ an then the NTSB and even the district court must defer to the agency that wrote the regulation for the interpretation. Yes, it's a digusting miscarriage of the checks and balances of the Constitution but it's not limited to the FAA regulations.