Based on the situation at the time, the struggle between Zhou Tian and that True God was essentially a contest between their lower ranks. It was a matter of seeing if Zhou Tian, after exhausting his own strength, could seriously wound the forces under that True God, ultimately preventing that True God from being able to protect themselves within other forces.
Evidently, although it was done unintentionally, given the situation at the time, Zhou Tian's ability did indeed disable part of the forces under that True God. Thus, even though the defense installations of the Divine City were still in place, they would likely struggle to exert their full strength.
Given the state of the Divine City at the time, if any force were to launch an attack against it, from every angle, it seemed that they might not have much resistance capability!