Same as any other economic system: power is usually concentrated around a very small group of people. In socialism and communism, that concentration typically occurs within the party leadership or central planning apparatus.

However, in free-market capitalism, anyone is allowed to participate in capital formation and accumulation. Ownership is not formally restricted to a political class. Entry into markets is open in principle (unless it stops being a free market), and capital allocation is decentralized through free and voluntary exchange rather than administrative decree.

That does not mean capitalism eliminates power concentration, as Wealth can accumulate and translate into political influence. But the mechanism of power differs: In centrally planned systems, control flows from political authority. In market systems, control flows from voluntary transactions and competitive success.