The more I think about it, the more I realize Daikokuzan is absolutely essential to the story

Even if Daikokuzan is slow, what makes it so terrifying is that no matter how good a city's defenses are, it's only a matter of time before it inevitably breaks through. It doesn't matter if the city's defenses are flimsy as hell like humanity's, or practically impenetrable like the NE's.

Realistically, when the world has gone to shit and the outside is dangerous, the best survival strategy is to fortify a location and hold out behind your defenses.

But Daikokuzans prioritize attacking and devouring cities with all the infrastructure necessary to maintain an ironclad defense. This means that just the existence of Daikokuzan is enough to make both the NE and humanity realize that "If we just hide and defend ourselves, we'll eventually get breached and fucked anyway."

We've already seen this happen with the former human fortresses, the Madalans' ship, the Neo-Humans' city, and the Spiral Mountains.

Ultimately, a passive approach simply isn't viable for survival. Daikokuzan throws the world of Versus into even greater chaos, preventing the story from stagnating into a series of defensive sieges.

This Gigantic Walking Disaster essentially pushes both the NE and humanity out of their shelters, forcing them to actively fight their enemies and seek out other ways to survive rather than just sitting back and relying on their defenses.

In other words, Daikokuzan is the embodiment of the pressure that makes simply turtling up and waiting it out impossible.