You'd think with the introduction of Im-Sama, people would realize that the "Balance of Power" has been a farce all along. It's purposely created by the World Government. It's nothing more than a facade, just like "No one sits on the Empty thrown." They want everyone thinking there is some perfect balance in the World, when in reality, there is but a singular true power in the World. Just like Im-sama dictates the Celestial Dragons, and the Kings and Queens of the allied Countires, the World Government as an entity dictates who supports this supposed "Balance of Power."
Who is it that decides who can become a Shichibukai? The World Government.
Who was it that stood back and did absolutely nothing while Blackbeard rose to power as a Yonko? The World Government. They wanted him to become a Yonko for this "Balance of Power".
Who was it that decided on who the new Yonkos were once Big Mom and Kaido were taking down? The World Government. Hell, they even went as far as to declare some low tier Pirate, who was apart of a rag tag alliance as a New Yonko. Buggy himself holds no strength, but with the inclusion of Crocodile and Mihawk, the Cross Guilds name holds weight. This man was declared a Yonko, because the World Government deemed it so.
The World Government dictates all of this, and by extension, Im-Sama is the Supreme ruler. The World government just doesn't want people to know that, otherwise they'd face a World wide revolution. So they play like there some magical balance of power that keeps the World running, and they are on the side of good, that keeps the Pirates in check, but in reality, they are the one True Power.