Although the former Dragon Emperor was invincible in the Heaven, he was still at the same realm and level as them. Also, though the power of the law of domination was strong, it did not completely overwhelm the laws of the other Divine Kings. At best, the Dragon Emperor was a tad bit stronger. Yet, the Dragon Emperor who had spent dozens of eras escaping and hiding in the Land actually appeared with such a crushing power!
Only after death could one understand and gain eternal life, thereby becoming a true god. The Four Divine Kings who were scared of death were all wrong from the beginning. Although Simba was the Dragon Emperor now, he still had Simba's old bad habits.
When the Divine Kings' laws dissipated and all their rule manifestations and powers turned into nothingness, the Four Divine Kings became no different from ordinary people. In Simba's eyes, they were merely four ants.