Although Duan Ling Tian was able to transform into a Nine-clawed Dragon Warrior, it did not mean that Xie Zong was afraid of him. He was only afraid of the Nine-clawed Divine Dragon supporting him.
Not only that, in Xie Zong's eyes, Duan Ling Tian was just like an ant even if he was a Nine-clawed Dragon Warrior!
In the history of Dao Martial Saint Land, there were many Seven-clawed Dragon Warriors and Eight-clawed Dragon Warriors that accomplished nothing. This was because being granted the ability to transform into a Dragon Warrior did not mean it would raise one's innate talent. They would still have to rely on themselves in regards to innate talent. The ability to transform into a Dragon Warrior would only grant them greater combat ability.