The state wasn't always mediating between bourgeois interests. In the 19th century, the state represented the interests of the bourgeoisie in general, such as providing a police, disciplining the masses, suppression of revolts, etc. - only later in the imperialist stage the state was forced to balance out competing monopoly interests, but my point is rather that the state back then was much more dislodged from capital as it is today, in neoliberalism. This is why I don't agree that just because the state transforms a public asset into another legal form, a public company of which it holds majority shares, doesn't mean the state retreats, it just merges with capital. This is why social democracy is impossible today, back when FDR and the British Labour Party after WWII were elected, the state still wasn't the same as capital. In state monopoly capitalism, this distinction is harder and harder draw (there will always be a distinction but it's much harder to find). I mean, today, it's easier to imagine a literal war with China than to imagine the American government nationalizing a single power plant.
>Monopolies are still market forces, just in an advanced stage.
True, I should have used the term "free competition".
>This is an excellent assessment. But then, what specifically differentiates neoliberal and socialist centralization? Does it hinge entirely on who owns the monopolies and the means of production?
Yes, but you could also imagine corporations with huge employee ownership participating in this, the necessary rupture is simply a proletarian revolution that disentangles monopoly capital by turning it into public property that is rationally planned, e.g. where value indicators are mere book-keeping metrics, and where production is not organized according to value realization on the market.