Fourth-Stage Cultivators were not invincible; they couldn't even dominate the human world.
Whether it was Mr. Chuan or You Jiu, both were strong in attack but relatively weak in defense. Their individual combat power could rival a Formal Mage Corps. If there were no Transcendents restraining them, with their strength, they could even forcibly take down any Formal Mage Corps on Earth—provided they had sufficient combat experience. However, the premise was that they had to engage in guerrilla warfare, not direct frontal combat.
Although their Protective Spells were not much weaker than their Offensive Spells, the individual firepower on Earth was enough to pose a threat to their Protective Spells. Under a barrage of bullets, a Fourth-Stage Cultivator's Protective Spells would still burst.
