Is “The divine strategist Xu Maogong” true?

In "Sui Tang Romance," Xu Maogong (Li Ji) is depicted as a semi-immortal Taoist strategist who is proficient in yin-yang and uncannily accurate in divination. However, the true records in "Old Book of Tang: Biographies of Li Jing and Li Ji" show that Li Ji (originally named Xu Shiji) initially assisted Li Mi, later submitted to the Tang, served through the early three reigns of the Tang dynasty, defeated Xueyantuo, pacified Goguryeo, and served both as a general and a chancellor, truly an outstanding famous general of his time, vastly different from the Taoist image in the romance. "Journey to the West" also writes his assertion of a dream omen: "此梦告准。须唤魏徵来朝，陛下不要放他出门，过此一日，可救梦中之龙。" ("Journey to the West, Chapter 010")