This is not true. States experience selective pressures just like any organism, and they can be more or less fit to their environments as a result. For example, before the advent of brass cannons in Europe, the invulnerability of castles in war meant that smaller, decentralised polities were favoured over larger ones. After about 1453, however, cannons (which nullified the advantages of castles) enabled the rise of large, centralised nation-states ruled by the powerful 'new monarchs'. Any smaller states in this era who tried to resist had their fortifications rubbled and forcibly annexed.
This is a simple example, but similar selective pressures apply to modern states - whatever system 'works' is dictated by the contemporary political and technological environment. To believe that it's simply about some kind of vaguely defined 'competence' is wildly ignorant of the reality of the global system.