Or do they simply need a common cause? (BRAINS! ...and other giblets)
Do bacteria or viruses need a hierarchy?
I suspect there's LESS than meets the eyes. We tend to project order onto randomness (seen any good clouds lately?)
Let's not make that mistake with Reavers.
Maybe they're just wild & violent. ...and honnngry.
No one can fly a ship- even a ship OPERATING WITHOUT CORE CONTAINMENT- without some kind of coordinated effort. The Reavers must have leaders, even if they are simply the ones who kill their way to the top.