Global use of bitcoin


What happens if bitcoin is globally adopted? What’s to stop the major corps from hoarding. Does bitcoin even really stay decentralised if 5 of the biggest companies on the world control a large % of the liquid supply?

As we know already the money always flows upwards, the most in demand products/companies always end up with the cash. I don’t see how this changes with bitcoin?

Please enlighten me, I wish only to learn more.