I'm amazed that the RAF managed to get along for 70-odd years before fitness testing came in!
It proves very little; those that enjoy phys get a kick out of showing people how fit they are, those that don't enjoy it endure the chore of maintaining a level of fitness that doesn't actually improve their effectiveness or efficiency.
It's become an empire that is increasing stress levels on large numbers of people, with little real benefit. It is held up as the RAF being concerned about your long term health, this is the same RAF that has little concern for your long term employment!