You are presenting this as if people can only spend as much on business ventures as they have in their wallets. If that were the case, then indeed companies could get big enough for nobody to be able to come up with the funding to compete with them, and wealth would concentrate. But one of the fundamental aspects of capitalism is that it offers access to funding. New businesses can be financed with credit. That defeats the economies of scale argument. Any business can have any scale from day one.