Guess the point of contention is whether a particular type of business class service (with flat beds, leather seats, etc.) forms part of the carriage contract. Undeniably these do not appear in the conditions of carriage and airlines protect themselves well by ensuring they contain the small print to "reserve the right to substitute aircraft for operational reasons".
But if the airline publicizes widely a particular type of service on a particular route, and it's the main swaying factor for someone to choose that airline over its competition, then arguably it should be a condition precedent and that carries some legal ground.
Only way to find out is for someone to take the airline to court to provide a precedent judgement.