"One cannot be a leader without first being powerful--without first having the physical and mental constitution capable of sustaining the burdens of leadership."
Tell that to anyone with a terrible middle manager. Or anyone watching Trump blunder his way into the front running for the GOP. Or to these 11 rules crowned while they were still in diapers: http://mentalfloss.com/article/12252/11-monarchs-crowned-while-they-were-diapers
There's really no shortage of rulers throughout history who absolutely had power, yet were not physically or mentally capable of handling it. These usually create the worst atrocities in history.
So yes, society absolutely does grant power. Power can also be taken, however usually society resents that and works against it.