Nice idea, but why would pirates and other criminals form a power? Everybody would want to be the pirate king and everybody would rob/pirate/kill everybody else - or at least try doing it.
The moment the organization becomes stable enough to offer sanctuary, banking, insurance etc to it's members it would simply become a normal state.
BTW: There is already one power that has the structure and organization of the mafia - an organization similar to the old roman empire. Just saying…![]()
Because criminals have families too and they have to provide for them within the context of a criminal organization. That's why even in RL the more organized (criminal) hacker groups have a payroll, benefits and an HR to administer them. Same structure, different end goals.