I'd say the real crux of the argument is in full centralization and collectivization, or full horizontalism and decentralization. The endpoints are different, so the means are different.

Either way, I don't agree that administrators represent a class. Public property is not bourgeois property, it doesn't exist in the M-C-M' circuit of production, it's collective and planned. Even if there's administration, it's a physical, real thing. There will be flaws, there will be issues, but to let perfect be the enemy of progress is an issue. It's less about some metaphysical "will of the workers" and more about material relationships to the means of production and the sublimation of property.

Secondly, the state doesn't "preserve itself," at least the Marxist conception of the state. The state isn't a class, it's a representative of a class, and when all property has been sublimated, there is no class, and no state. There still exists administration, but not special bodies of armed men to oppress other classes, as there are no classes to oppress.