Infanteer said:
That's a logical fallacy. Circumstances far beyond a neutered monarchy go into making these countries the "best". We can start with uninterrupted rule of law, lack of open warfare within the country, and prospering under the American nuclear umbrella during the Cold War.
And all but the latter could be, in one way or another, linked to an apolitical and inherited head of state position.
There's certainly other ways to keep a country in decent shape; long-established usage and custom, diffusion of control over the major organs of state, and Politburo-style committee rule; but an established monarchy is certainly one of the more common ways to maintain stability in a country.
Monarchs are, generally, creatures of stability: the idea is to hand the job and the country down to the kids, complete with palace, treasury, jewels, and so on. There's certainly outliers: North Korea's Communist dynasty comes to mind; but, generally, the crown has a need for real good government, if only to keep things sweet for the royal family.
It also seems as if it'd be harder (not impossibly, but harder) for an upstart political movement to seize absolute power or start a civil war when a nation's military owes its loyalty to King and Country, rather than either more easily re-defined symbols, like a constitution, or to one elected office or another. I'll offer Mussolini as an example where this
didn't work, and Thailand as a contemporary extreme, outlier example of this in action.