Having royal blood is not like having charisma. If you were of royal blood in those times it meant people followed you because of that fact alone - charisma or no charisma.
The same is true today. In every "democracy" or "republic", the elected power structure holds the reins only so long as the army agrees. Even here in the US! After all, let's say Congress passed a treaty signed by the president requiring everybody to turn in their guns to the UN, or to abort their third child, or to become part of the Global Union. Do you think the US Army would let that happen? If you do, you're wrong. Sure, the top brass would probably go along, but some charismatic colonel somewhere would rally his men and roll the tanks into Washington D.C. It's called the "Seven Days in May" scenario.
In America, we call people with charisma "born leaders". You mostly see them on the football field, the movie set, at the head of the Boy Scout troop, and in other, similar locations. But given the right set of circumstances that popular quarterback, beloved film star, or Scoutmaster could be a Charlemagne, a Joan of Arc, a Francisco Franco.
This is one reason why I am a monarchist and an opponent of so-called popular government. God knows His own, and gives to some men -- as He did to the shepherd David -- the power to inspire the hearts of others. Those who dare topple a king -- even a bad one -- are going against the will of God. "I will not raise my hand against the Lord's anointed" -- 1 Sam 24:10