[Suppressing Emperor Momentum]
Momentum, another name sometimes used for aura, can be used in various ways. And Di Jiaying created a method or technique based on it that is unique to her.
Throughout history, no mortals could be said to have defeated an Emperor–no matter the circumstances. After all, although Emperor Three Leaf sealed his power to be the same before he proved the Dao, it did not change the fact he was a higher being.
He had seen the higher existence of the Law or Dao. Even with the same strength as his past, his understanding and control of Dao were the same. But, even then, he still lost to Di Jiaying.
Her victory against such an existence gave her unparalleled pride, confidence, luck, and destiny. Why did Di Tian choose someone with a Tyrant or Overlord Dao as his general? Why not choose someone with a War or more military-based Dao? Or, just someone extremely powerful and talented?