The Ixians have their technology, and the Tleilaxu their genetics. The Imperium has armed forces and planetary resources(and manpower), and the Guild has its space travel.
How really are the Bene Gesserit powerful?
Of course they are very accomplished and super-cool in themselves, with prana-bindu and the vast wealth of scholarship. But how do they hold sway over others? What clout/resources do they hold which will get them things they want/need from others(other players)?
The only things I can imagine is, the aristocracy of the Imperium patronised them for the breeding and the training etc. they provided. The God-Emperor had them on welfare throughout his reign. Also maybe, the followers of those religions they toyed with provided them with some tithes etc. I imagine.
But how did they manage to be such a power in the universe? What did they have to keep themselves going and expanding? Especially after the translation of the God-Emperor?