It's been a political concern in the past, yeah. Aura-having nobility ruling over powerless peasants. Thing is, anyone can learn to use Aura, and a thousand peasants with Aura and sharp sticks will beat a dozen knights with Aura and a fancy gunsword. Especially when you account for Dust, which anyone with even a whiff of Aura can use as well as anyone else. Or, really, anyone after firearms were invented.

These days the ruling class has pretty much switched over to money instead, for oppression purposes. That at least has scarcity going for it.