The Vicky companies in Diamond Age are basically John Company, the British East India Company, I think it even more or less says as such, calling it John Zaibatsu. The Victorians appear to live in a plutocracy, but it's very particularly a Victorian plutocracy, we don't see any poor Vickies, the thetes living down in the LT are not Victorians and nor are the artisans on the hillside. The nature of the Mandarins is unclear, whether Doctor X is unusual in operating an actual business close to the LT, or whether actually the Middle Kingdom, too, is controlled by businesses and the Mandarins are the owners.

And as to the idea that it became true, well, here in the real world it is Russia that invaded Ukraine and not an invasion by Gazprom or whoever. The sovereign entities are still fundamentally concrete in a way that a corporation is not.

The Fists in Diamond Age may in some sense be tools of the Mandarins, but certainly the Mouse Army don't work for anybody except Princess Nell, their loyalty to her has been blended into all their learning from infancy, almost without anybody consciously intending this (Hackworth is ultimately responsible, but if/why Hackworth chooses Nell rather than his own daughter is unclear, we don't see enough of the other copies of the Primer to discern whether the other two girls could have led the Mouse Army, the novel is about Nell).

The land war between Russia and Ukraine that's happening right now, and the decade+ of land war the US waged in the Middle East before that, make me think any bickering between Google and Apple still look worlds away from corporate-conflict dystopia (of course, this is a critique that also applies to Snow Crash and The Diamond Age, which were corp-heavy).