Ye Silang had escaped from the clutches of Immortal Peng, not because he possessed extraordinary willpower, but because he quitted before completing his training.
Both the Heartful and Emotionless Sword techniques comprised of seven stages, and both Ye Silang and Chu Yangjun had stopped learning after mastering the fourth stage. Therefore, even though their sword craft was very good, it was still far from the very best. They would not have fallen under the killer's sword if they had mastered all seven stages of their training.
As with Gu Shenwei, Ye Silang had already been trained in other forms of kung fu before coming under Immortal Peng's tutelage. Ye Silang had always been tied down by worldly concerns and had left the pavilion once he felt that his sword craft was good enough for him to survive in jianghu, on the pretext that he would return after his travels. Instead, he had returned to North City.