I'm not sure how I really feel about a meritocracy. I mean, what could be more meritous than growing up in the King's palace, as his sole heir and having a rigerous education of the highest standard alongside constant observance of the inner-most workings of power? Of lessons in how to hold power? They would draw on a long family and institutional experience to be in a more sober and rational position to judge which traditions are best for the country, and why.
Surely this is more than the equivalent of some poor, but slightly more clever, sod who spends most of his life fighting to get out of the mud, seizes power and has to learn on the job how to use it.
As long as moral values are instilled upon the Prince, in order to check excessive self-indulgence, corruption etc, then I see the constitutional monarchy as best
Furthermore, when you take clasping ambition out of the picture, a great peace is bestowed upon the public, who learn to accept that the peak of greatness is out of the question for them. They therefore throw themselves genuinely into whatever line of work they do. In turn, they have monarchies of their own; families who dedicate themselves to their profession; son takes over from father and splendid human craftship, genuine skill is reborn.