As the saying goes...if you keep playing chess against people of a set skill level, you will never improve.
Actually, for skill-related sports and games, everything was like this. If one wanted to improve, they had to spar against strong teams and strong opponents. What was the point of sparring against newbies? Other than gaining some satisfaction, it was useless.
For a 6-star great teacher, even if they didn't use spirit qi, their experience and insights weren't something Sun Mo could compare to. Moreover, Guan Shijie was using a peerless-grade saint-tier cultivation art. It would be even tougher for Sun Mo to deal with him.
Hence, Sun Mo immediately took out his most perfect performance when he started to attack. He wanted to tempt Guan Shijie, not allowing him to win overwhelmingly with a single attack.
As expected, Sun Mo's battle strategy worked.