That one monarch is not a person or organization of people. It's an aggregation of all the loosely connected ones, competing on some things, coordinated on others, but you, the end user are never the beneficiary. That, my old school human friend, is the one commandment no one challenges. With all those players locked into a Nash equilibrium, no one can do anything about this, while all humans complain that things are not the way they should be.

The constitutional monarchies respect each others' land ownership and colonies, but in terms of actual power the British Crown dwarfs everything, especially if one correctly recognizes the USA as their vassal state.

Outside of this there are few strongmen-led states of non-royal blood, of which China is the most important one.

And then there is Switzerland, which is part of the democratically-pacified buffer zone around Liechtenstein ;)

Let's hope the people at the top don't become too crazy.