Agreed to a point. The "middle of the map" theory only applies if you assume economic activity is relatively evenly spaced (which it mostly is). Unfortunately this representation won't tell us much about where economic activity really is.
There are better ways to represent the information presented. A 3D map would put economic activity somewhere in the middle of the earth, but you would eliminate the "starting center" bias.
3d would be pretty hard to see. But there's plenty of empty spots on the earth that are in the middle of all economic centers. Ideally bordering every economic center ... since economic activity (and land mass, which is likely why) is concentrated in the northern hemisphere, why not center the map around the north pole ? No economic activity, roughly equidistant of the 3 big centers. Sure it might not be perfect, as South Africa will effectively be counted with Europe and Australia with Japan, South America with the US (well, with California effectively), but it ought to be a bit better than this.
If that is still less than optimal, maybe try the south pole ?
There are better ways to represent the information presented. A 3D map would put economic activity somewhere in the middle of the earth, but you would eliminate the "starting center" bias.