This is a fallacy where you extrapolate the large change in a single dimension and imagine everything else staying mostly the same, ignoring the disruption of the system from non-linear effects of that single dimension being saturated. When a few companies capture a large proportion of the economic value of the system, the economy simply doesn't exist as it is currently conceived.
The current economy is driven by the need for broad participation to maintain the collective standard of living. We all get to skim a bit of that value for ourselves, and so distribution is inherent to the system. When broad labor participation is no longer needed to create collective wealth, the leverage of the average person to demand a share of the value produced evaporates. The economy in this scenario is something very different. There's no reason to imagine wealth being distributed in an egalitarian way; it certainly won't be automatic.