Shōgun, FX’s runaway hit of a historical epic set in feudal Japan, aired its final episode Tuesday. By the end of the saga—a fictionalized tale loosely based on the birth of the Tokugawa shogunate, adapted from James Clavell’s 1975 novel—the Englishman John Blackthorne has not found the deliverance he seeks. Marks: We felt there was a little bit of, I …