In defense of people who believed this, they were thousands of years away from anything being better on earth.
Like imagine living through the decline of a brutal slave empire, which took centuries to fully collapse, and the thing that replaced it was fucking internecine Feudal warfare for another millennia.
Unironically, whether you can stomach all the atrocities that happened afterwards or not, until the rise of Islam and its golden age, you would be pretty justified in thinking the world was never going to be better than it was in an age when most people were still utterly miserable.
Not for lack of trying.
Did we all just memory hole that he tried to start a war with Iran this year?