>>96138201
>It does center around the primarchs and the emperor, the whole conflict stems from the fact that the primarchs don't like emperor's ideals and decide to betray him.
that's the starting point, but not what most of the books are about. You don't know it because you haven't read them.
Primarchs barely appear and most of the stories are told from the PoV of space marines or humans.
in fact, the number one complaint about the series among the actual readers is Horus being absent from it, besides a couple books.