There will be an oversupply, demand will be there too, but no one can afford to buy since most jobs have been replaced by AI. So the price of goods and services should go down, or some form of UBI will have to be implemented which is just socialism for the masses. Its either that or total anarchy (also socialism).
If humans remain in control of it, then how can it possibly lead to anything other than extreme oligarchy?
Depends on the distribution of such AI. For example, if everyone on Earth has their own, personal superhuman AI, it would not lead to extreme oligarchy. If only a handful of humans control superhuman AI, it would.