You're directionally right, anyway. There's no reason significantly advanced AI (likely to not be developed from LLMs but from some other path) can't completely replace a wide variety of human labor. But replacing human labor with machinery (i.e., capital) is not new, it's been going on for a couple centuries plus some. The thing that happens when you replace wage labor with capital is that the rate of profit (i.e., the ratio of profit to the amount of invested capital) tends to fall, which is a systemic threat to investment. The recurring tech and asset bubbles since the 1990s have each been inflated in an attempt to maintain rising levels of investment in the face of rising productivity and therefore falling profit. An economy of dark factories isn't useful under capitalism, because it produces goods which end up having no sale-value.