Zheng was immensely strong, both in body and spirit. Having survived countless life-and-death battles and witnessed the deaths of many comrades, especially after overcoming his inner demons, he had become almost invincible. Though not yet powerful enough to disregard other Reincarnation Squads, he could certainly be described as superhuman.
But he was not omnipotent...
The world of the Reincarnation Squad is not one that can be overcome by heroes alone. Here, individual heroism often signifies ignorance and foolishness. Against ordinary Reincarnation Squads, this might be manageable, but against teams with thinkers like Neos or Julian of the Team Pacific, such heroism would bury their own squad. Of course, if "power" reaches a certain limit, like the Demon Reincarnation Squad, then even the greatest wisdom loses its effectiveness.