That seems to depend on the size of the world economy. There may be an absolute minimum of organizational ability for some complex entities to exist - Toby Ord points out that if the human population was much smaller, we wouldn't be able to create the infrastructure that allows for computers.

If the absolute structure of an easy to create Superintelligence requires hundreds of millions of agents in concert, it would appear that a large fraction of the economy is necessary for an observer of a world with a few billion people.

A more obvious note is that the closer you are to representing half the economy, the easier it is to reach the point in which you control 51% of it (which may coincide with strategic advantage in some cases).