So, apparently the Vance family used to be rulers of the world until the gods took that title away from them and instead set up the Queen's Blade tournament. Just what did they do that warranted the gods themselves proclaiming hereditary monarchs would no longer be allowed, and instead that Queendom would be given to the last Action Girl standing at the end of a women's only combat tournament, with them only able to reign for four years before they must defend their title or forfeit to the new winner, with this being enforced by threat of Heavenly punishment? Just how bad were they that this current system, with all its possibilities for abuse and bad rulers, is considered a superior system?
It's heavily implied (at least in the animated version of Rebellion) that the only alternative besides the monarchy and the tournament is just plain anarchy, as we can see in the second episode of Rebellion TV series. Also, it's heavily implied the whole Continent's society is somewhat semi-barbarical (albeit not at Conan the Barbarian levels), so the population of the Continent just simply loves to fight or at least watching someone else fight, so the tournament is simply an outlet for releasing their (or their daughters) violent impulses without relying on waging a war. This is somewhat evident as neither Hinomoto, nor Amara and Shai-Fang had any equivalent to that tournament by themselves, despise being warrior-based societies too and they have to go to the Continent if they want to enter into a fighting tournament.