Su Yang didn't kill Master Fang because Master Fang's magic was not bad, and it could still be of some use to keep him around. Moreover, Su Yang had cultivated on his own, and he didn't understand the affairs of the cultivation world, so he wanted to learn more about the cultivation world through Master Fang.
Although Master Fang's magical skills were not very exquisite, he had been cultivating for a long time and knew quite a lot.
After chatting with Master Fang, Su Yang finally learned that in the world today, there were actually quite a number of cultivators. However, very few of them really achieved significant success in cultivation. Someone with the power of Master Fang could be revered in a single city.
If one were stronger and stepped into the Fusion Realm, one could be revered across an entire province. At the peak of the Fusion Realm, one would be an entity respected by tens of thousands, known as The Sovereign!