Its true !! I've personally seen many engine that have used many different types of coolants but none of them have had the protection like an engine thats had genuine subaru coolant in them all its life (some subaru engines with 300k)

BUT... if the engine has had some other coolant (not genuine) in it, the damage is already done its doesn't take long for aftermarket coolants to breakdown !! ITS LIKE THE OLD SAYING "YOU GET WHAT YOU PAY FOR"