Actually, on a more serious note, I know some roleplayers who are obsessed with this question and keep this speculative document going to try to answer it. As a lore archivist, my answer is usually entwined with the nuance that Square Enix wants you have some excuse to sensibly see yourself as any job you want to be. They deliberately leave loopholes open, so even if we can Pirates vs. Ninjas a list of more vs. less accessible jobs together, at the end of the day the most difficult one to get a hold of is just as "likely" as the easiest, from a certain point of view.