Anarcho-capitalists don't see capitalism as a power structure though. They see it as something natural that emerges organically, without it being imposed on top. They argue that, for example, markets appear in failed states, they emerge even when the states try to suppress them (black markets), and they're a natural outcome of different skills and needs. So it's not a power structure any more than say, mountains are a power structure, even though some people can exploit mountains pretty effectively to gain advantage.