The strength of the Heavenly Prince is actually not weak; in terms of combat power, he is not much different from the Leader of Tongtian. His mistake lies in using a sword in front of the Leader of Tongtian!
The power levels in the Yuan Realm are much higher than those in the Three Realms, but in some areas, they fall far behind the Three Realms, such as the Way of Transformation, and also the Sword Dao.
The Leader of Tongtian is the Ancestor of Sword Cultivation in the Three Realms, and his mastery in the Sword Dao has reached an unparalleled level. Even the Hong Jun Daoist Ancestor admits that his swordsmanship doesn't compare to that of the Leader of Tongtian. For the Heavenly Prince to use swordsmanship against him is like showing off an axe before a master carpenter, how could he not be defeated?
"The strength is good, but it's too foolish!"