Cultivators couldn't fuse with the Fengyun Realm and then control its Origin Power. Even Ling Tian found it difficult to do so. He could only draw upon a tiny portion of the Fengyun Realm's Origin Power, and that had little effect on their battle against Venerable Sword Saint.
However, just because Ling Tian and the others couldn't do it didn't mean nobody—no, no living being—could. Saint-grade Heavenly Treasures could, at the very least. More importantly, there were quite a few Saint-grade Heavenly Treasures around them. Although they were only assisting from within Ling Tian's Small World, they had greatly strengthened his connection with the Fengyun Realm, allowing him to draw upon a much greater supply of Origin Power. As a result, his control over the Myriad Sword Demon Extermination Grand Formation's attacks grew considerably stronger.
Of course, most importantly, the two Enlightenment Sacred Trees were using the power of the Soul Law to suppress the Soul Slaying Sword. This made it much easier for Fairy Meng Shang and the others to withstand Venerable Sword Saint's Soul Slaying Sword attacks. Even Tan Tai Xiao Lin, whose cultivation was the weakest, could now handle them with relative ease.
Seeing that everyone could withstand the Soul Slaying Sword with relative ease, they were all greatly encouraged. In particular, seeing Venerable Sword Saint's strength diminished by quite a bit under their suppression gave them greater confidence that they could drive him back. Though they were confident they could force Venerable Sword Saint to retreat, killing him was almost impossible. After all, he could escape with ease, and Ling Tian and the others had no way to stop him.
Of course, all Ling Tian and the others needed was to drive Venerable Sword Saint back. That would give them more time to improve their strength,