I agree that people who are actually very serious about runing a vacation rental business need to delegate their tasks. Running all the properties yourself is indeed very time consuming and if one tries to do so, he or she will quickly reach the ceiling above which it will be impossible to get unless one starts delegating.
Hence it's indeed better for a business owner who already has experience in owning rental properties to find a subcontractor who will take care of all the calls, reservations, cleaning and etc.