"Judging from the outcome, the Destiny Demon is not as formidable as the Space-Time Demon. In the Prehistoric World, the River of Destiny is beneath space and time, and their disparity in strength is evident."
The Great Dao inherently has no distinction of high or low, but the Chaos Demigods who wield it vary in strength. It is precisely because of this that the Great Dao is perceived to have strength disparities.
It is not the Great Dao that is strong, but those who wield it elevate it to a supreme level, thereby creating its strength.
The strength of the Great Dao can be seen in the structure of the Prehistoric World, the more foundational a Dao is in supporting heaven and earth, the stronger it is. Because during the creation of the Primordial World, they contributed the most effort, hence they are the strongest.