In recorded history there have been plenty of economic setups that have very few or no downtrodden. You just gotta go and read anthropology. Another thing to take into account is where we are as a society - and where we can go. Both with automation and gear we can make such work easier, and in a society where we have more control where to direct research (as opposed to VCs seeking maximum profit) we can focus on solving bad jobs like that. Finally - incentives. Why have someone be a coal miner so that their kids do not have to starve, when we can have it be an exclusive and hard workplace, that is both celebrated in public and comes with the pay package of a director or executive. The coal miner certainly does more and more useful work than the average tech founder.

But I agree UBI is not the final solution. The final solution involves stuff like abolishing wage labor, circular economies, non-transferable labor-time tokens and democractic management.