Are you assuming free trade then is available to Japan? IIRC their assumption wasn't just to get the raw materials out of their sphere, but to have old style European colonialism with market preference for their exports. So their trade block would mostly not participate in the global market except on a limited basis. I assume they would take all of China at some point as that was their goal. In that case they have a very large chunk of the global market, but the issue is that it would remain less industrialized than it would become IOTL because of keeping the much larger area subordinate to Japan's economy, rather that it participating in the global trade structure. I doubt it would dominate the global economy because of the less than competitive Japanese industry practices at the time, their lag in innovation at the time, and probably the lack of willingness of the rest of the world to trade with them on a large scale basis. In fact the global economy is actually retarded by these trade blocs, as they cut off free trade and development of a global economy, as there is a lot of duplication of effort within the trade blocs and the blocs are structured to the benefit of the dominant power; one of the major charges levied against British colonialism is that it retarded the economic growth of places like India because it kept it subordinate to British industrial preferences, rather than letting the Indian economy develop on its own and find its place in global trade for its own benefit. China and the rest of the sphere would have the same problem ITTL, especially as Japan slaughters to political subdue the Chinese and other peoples to make them conform to Japanese culture and political preference. If anything the great co-prosperity sphere would end up being a mess like a Nazi dominated Europe would be, but moreso, as the Japanese have less population than their dominated peoples and would need to use even more slaughter and repression to keep it subordinated.