Earlier quoted context omitted.
Antitrust law does exactly this. If Amazon owning EA overly concentrates market power/forms a monopoly, it'll be rejected and the deal with fail. Why would you want to put an upper cap on the size of companies? It feels like stifling innovation and productivity, which will be overly negative for everyone.
It seems to me most innovation comes from increased competition and upstart companies. Do large conglomerates provide the main driver of innovation?
Meanwhile, companies that leverage existing technologies in new ways can be innovative with much fewer resources - e.g. your typical web startup.