The Human Emperors had the same equal level of standing with the heavens!
The heavens referred in this context meant the ancient will of the Immortal World!
During ancient Immortal times, as long as someone was a Human Emperor, regardless of their cultivation level, he or she would stand on the same level of existence with the heavens themselves!
However, ever since the two Immortal Halls instigated the Great Deification War, there were no more Human Emperors in the world after King Zhou!
It was said that later, after that great calamity, someone known as King Qin tried to restore the Human Emperor's name to its former glory. Alas, he failed in the end.
That made King Zhou the final Human Emperor in the world.