He had to figure this step out. Kadin's sword attack left a very deep impression on Wang Zhong and inspired him. Previously, Wang Zhong had been trying to stabilize and stack his Soul Power, but the effects weren't very good.
Wang Zhong's maximum Soul Power limit was around 11,000 Grassos now, but it would be extremely hard for him to stack it until 12,000. Based on this figure, his power was inferior to that of Kadin, who certainly put in a lot of effort into revising his attacks.
Wang Zhong's supreme control of Soul Power was definitely unprecedented, but that referred to his control on the micro-level. However, if he wanted to stack his Soul Power, that would be a macro-level technique, and his delicate micro-level control wouldn't be of much help.