True, but it would nevertheless make for a decent compromise. Do you have a better suggestion?

It isn't much of a compromise. It presumes enough coherence for everyone to agree on a supreme power that all shall obey, to divide the cake and enforce the borders.

To see how the situation is actually handled, look around you, at the whole world now and in the past. Whenever there is no common resolve to leave each other alone, then as has been observed of old, the strong do what they will and the weak bear what they must. Europe managed it in the Treaty of Westphalia, but it took thirty years of slaughtering each other for them to decide that no-one was ever going to win, and draw up a massive agreement to disagree. Best of luck getting any such agreement today between (for example) jihadists and everyone else. Or SJWs and neoreactionaries. Adding superintelligence would be like squabbling children getting hold of nuclear weapons.