If everything that a human can do, a robot can do better and cheaper, then humans are completely shut out of the production function. Humans have a minimum level of consumption that they need to stay alive whether or not they earn a wage; robots do not.
Since most humans live off wages which they get from work, they are then shut out of life. The only humans left alive are those who fund their consumption from capital rents.
If humans who don't own robots are not producing and therefore not earning, then they're also not buying. Who are the robot owners selling their products to?
See: "build me a bigger yacht", building moon bases, researching immortality medicine, and building higher walls and better killbots to manage any peasant attacks
Why would other robot owners need to buy anything? They can just get their AIs to figure out how to make the things they're buying so they can not buy them anymore.
I think it's likely that there'll still be specialization - some robots/AI will be better at some tasks than others. On top of that, physical/natural resources may be owned by different people. So maybe you need tungsten and I need someone to build a space elevator, so we trade.
If everything that a human can do, a robot can do better and cheaper, then humans are completely shut out of the production function. Humans have a minimum level of consumption that they need to stay alive whether or not they earn a wage; robots do not.
Since most humans live off wages which they get from work, they are then shut out of life. The only humans left alive are those who fund their consumption from capital rents.