Dragon Rearing Sovereign's body was the corporeal body of a god, and with the addition of five dragons coiling around his body and two serving as his weapons, his strength multiplied several times.
Even though Dragon Rider Sect was founded by Dragon Rearing Sovereign, it only had the abilities to control unusual breeds of dragons and snakes; its people didn't have the abilities to borrow strength from dragons. But Dragon Rearing Sovereign's Secrets of Dragon Control could allow one to borrow flood dragons' strength for themselves.
Besides that, his Dragon Rearing Scripture didn't contain all the techniques he had, either. He had held back some information. Even though the Dragon Rearing Scripture in Qin Mu's hand was much more complete than the one passed on to Dragon Rider Sect, the most important battle methods were no recorded inside it.