KaiserChicken said:
Indeed, it's not hard to find historical situations where incompetent and stupid monarchs ruled over periods of extreme and stable prosperity, thanks to their trusted advisors.
In fact, it's incredibly hard to find any period in which monarchs were
either insane or incompetent that was not rife of instability, intrigue, and open strife. Even George III's insanity almost caused the fall of William Pitt the Younger's government.
Minorities are another issue altogether, since advisors and member of the Council of Regency were usually appointed by the late monarch's will (like Louis XIII of France) and things could be arranged when the monarch was remotely capable when legally adult (like Louis XIV or Karl XI of Sweden).
However, insanity and/or incompetence was most of the time irreversible, except by death or abdication of the monarch. Grandees, advisors and blood princes were left to their own devices and no one (save a VERY loyal Prime minister or Lord Protector) could keep them on the line. If not, usually it was open season for all the noblemen's personal inclinations and ambitions.
D.