What the Polymath attempted to do was to repeat human history, in part at least.
During the early days of the Age of Conquest, the Terran Empire rose up as a united human star nation that effectively mobilized every human under a single banner.
Just like what the Polymath wanted to do, the Terran Empire obeyed the rule of a single emperor who reigned with absolute power.
The reason why the humans back then supported this shift was because they were in an awful situation back then. Only by setting aside their historical regional and cultural differences would they be able to make the best out of their limited manpower, technology and resources and make real gains in the large and dangerous Milky Way Galaxy.
The Terran Empire was a success. It grew rapidly under the wise and competent leadership of the leading figures of the time. Each of them were heroes and visionaries who all made undeniable contributions in the rise of humanity!