Shack's account of ATC training in the 1960's speaks for itself. The arrogant, prejudiced attitude typified by his comment was rife in the ATC service at that time. There were some very sound types, but also a high proportion who could not grasp that given appropriate training, people with varied backgrounds and experience could become perfectly successful controllers.
Hardly surprising that a direct-entry ATCO with ten years military experience in ATC or aircrew was probably quicker off the mark than some of the early cadets after only one year of a three-year cadetship - he is not comparing like with like.
However, with appropriate training and experience, I doubt if there is anything to choose between the two, and that is the point - appropriate training - something that many of the mentors of that period were not very good at.
If we deserve the bosses of today, what did Shack and his contemporaries do to deserve some of the stuffed-shirted clots of the 60's, whose only skill in ATC was to fire a Very pistol?