Royalty is done in by inbreeding and unbridled envy from commoners towards excessive wealth but England was the richest most developed country for a long time. It's a good formula for a stable government that doesn't go bankrupt. If George Washington had become king, America would be a richer more conservative country today. If a designer country and constitution were engineered in modern times, a kingdom is a good way to go, but not with an affirmative-action leftist king!
Part of the Founder's genius. Look at what a loon Prince Charles has turned out to be. But he can't be recalled or voted out. Pity the PM who has to deal with him one day.