In front of an Immortal Emperor, people of the Emperor clans could do nothing. The methods of the Emperor clans that could threaten Immortal Kings were useless to an Immortal Emperor.
The Emperor clans could preserve an attack from an Immortal Emperor as their trump card but an Immortal Emperor could slash out thousands of such attacks at any time.
The Emperor clans relied on the methods left behind by the Immortal Emperors. However, the current Immortal Emperors were the source of power. They didn't rely on anyone.
Other than the four elusive great Celestial Venerates, they were the most powerful ones in the world.
Hence, to the Moon Empress, punishing a peak-stage Immortal King was nothing.
Even if the peak-stage Immortal King was just a step away from the Immortal Emperor Realm, this step was huge.