Neither humans nor computers have to use all of their capacity all of the time to do useful and high level work. The human brain with its 100 billion or so neurons uses little of its capacity for the activities we call thinking. Mass storage can also be used for much of the intellectual work of the professions. Standard procedures are followed again and again by doctors, lawyers, engineers etc. Professionals who deviate from standard procedures can find themselves in trouble with their professional associations.
Mass storage is almost unlimited and costs very little.
Its limitation is the slow speed of access. However, it is still fast enough to reach the necessary standard for the task at hand in many cases. For example, a physician will usually select a reference work off the shelf for prescribing drugs. It would be a waste of the physician's time, if not impossible, to memorize the thousands of prescriptions. Because it is untiring and error-free it surpasses human equivalency.