It might be necessary to concentrate wealth and thus economic power into a smaller amount of entities but why should so few have control over these entities? If the actual employees receive more benefits from a company doing well and a board of directors is not responding to the needs of a few shareholders but to the actual market need and the need of the company employees you would still have a concentration of wealth in the form of a company but with more participants. The employees would then have the incentive to provide quality labour because that in turn makes the company do well of which they profit directly.