Thunder Giants are the throne powers inherited from the ancestors of the Lei Clan, and when compared with the real thrones, they naturally aren't comparable. However, this still is a throne-level power, and opposing it is by no means easy.
Given the disparity in strength between the two parties, and the barrier of Wanqian Thunder City, the three Void King Wizards had no better strategy than to passively defend.
"Boom-Boom-Boom!"
Thunder Pillars, carrying overwhelming power, struck the exterior of the city repeatedly, like divine soldiers descending from the heavens.
Again and again, intercepted by the three Void King Wizards, each strike causing certain injury, something that Ivan and the others experienced profoundly, with a degree of suffocation in their hearts.
Helpless to change the situation, it's because the Wizards have yet to gather throne-level power.