The non-benevolent future is not self-defeating; we have historical examples of depressingly stable economies with highly concentrated ownership. The entirety of the European dark ages was the end result of (western[0]) Rome's elites tearing the planks out of the hull of the ship they were sailing. The consequence of such a system is economic stagnation, but that's not a consequence that the elites have to deal with. After all, they're going to be living in the lap of luxury, who cares if the economy stagnates?

This economic relationship can be collectively[1] described as "feudalism". This is a system in which:

- The vast majority of people are obligated to perform menial labor, i.e. peasant farmers.

- Class mobility is forbidden by law and ownership predominantly stays within families.

- The vast majority of wealth in the economy is in the form of rents paid to owners.

We often use the word "capitalist" to describe all businesses, but that's a modern simplification. Businesses can absolutely engage in feudalist economies just as well, or better, than they can engage in capitalist ones. The key difference is that, under capitalism, businesses have to provide goods or services that people are willing to pay for. Feudalism makes no such demand; your business is just renting out a thing you own.

Assuming AI does what it says on the tin (which isn't at all obvious), the endgame of AI automation is an economy of roughly fifty elite oligarchs who own the software to make the robots that do all work. They will be in a constant state of cold war, having to pay their competitors for access to the work they need done, with periodic wars (kinetic, cyber, legal, whatever) being fought whenever a company intrudes upon another's labor-enclave.

The question of "well, who pays for the robots" misunderstands what money is ultimately for. Money is a token that tracks tax payments for coercive states. It is minted specifically to fund wars of conquest; you pay your soldiers in tax tokens so the people they conquer will have to barter for money to pay the tax collector with[2]. But this logic assumes your soldiers are engaging in a voluntary exchange. If your 'soldiers' are killer robots that won't say no and only demand payment in energy and ammunition, then you don't need money. You just need to seize critical energy and mineral reserves that can be harvested to make more robots.

So far, AI companies have been talking of first-order effects like mass unemployment and hand-waving about UBI to fix it. On a surface level, UBI sounds a lot like the law necessary to make all this AI nonsense palatable. Sam Altman even paid to have a study done on UBI, and the results were... not great. Everyone who got money saw real declines in their net worth. Capital-c Conservative types will get a big stiffy from the finding that UBI did lead people to work less, but that's only part of the story. UBI as promoted by AI companies is bribing the peasants. In the world where the AI companies win, what is the economic or political restraining bolt stopping the AI companies from just dialing the UBI back and keeping more of the resources for themselves once traditional employment is scaled back? Like, at that point, they already own all the resources and the means of production. What makes them share?

[0] Depending on your definition of institutional continuity - i.e. whether or not Istanbul is still Constantinople - you could argue the Roman Empire survived until WWI.

[1] Insamuch as the complicated and ideosyncratic economic relationships of medieval Europe could even be summed up in one word.

[2] Ransomware vendors accidentally did this, establishing Bitcoin (and a few other cryptos) as money by demanding it as payment for a data ransom.