No, market cap does not come out of thin air. Money flows in one direction and human activity and real changes in the physical world flow in the other direction.

Nobody is mad about the billionaires having a lot of money - they are mad that people are pissing in water bottles to make their route, or having the city’s public infrastructure privatized, or the many other fantastic real world changes that are on the other side of these fantastical market caps.

Traditionally, the value of a security is a prediction of its future cashflow to perpetuity discounted by a capitalisation rate. While it is true that some securities these days are sold as something not dependent on future cash flows, and insiders are paid off by selling something misleading to retail investors, that is known as a Ponzi scheme and is traditionally prohibited by securities regulations.