The concentration of power is the monopolization tendency inherent to capitalism. That's how it works. It forces those in control of business to attempt any means of increasing the mass of profit and not get destroyed by competition. Monopolization does both of those things and business owners realize this quickly.

Capitalism is not the exchange of goods among individuals. That has existed for a very long time and includes feudal and slave and communal and really all systems we are familiar with where people interact with one another.

Capitalism is an economic system dominated by private businesses that employ wage workers to produce commodities for exchange. This differs from the systems it displaced, which were usually feudal, mercantile, that sort of thing.