I don't think you understand the point that I am trying to make.
Yes, the prime meridian is an arbitrary line of longitude. It is man-made. Humans decided to center the world around Greenwich in London. They could just have easily decided to center it around the Giza pyramids in Egypt, New York, Quebec, Tokyo, Auckland or anywhere.
The point that I am trying to make is: when you convert the Equrectangual map projection into the Peirce Quincuncial Projection you have to choose a line of longitude to center the projection. If you choose to center the map around Reykjavik in Iceland, you end up with a map projection that shows Ne Zaland as very far away from Australia. This is the image used on Wikipedia with Reykjavik in Iceland as the prime meridian of the Equrectangual map projection used to create the image.
However, if you use the real prime meridian in Greenwich London to create the Peirce Quincuncial Projection from the Equrectangual map projection. There is very small distortion to large land masses. The only areas of land that are distorted quite a lot are tiny islands in the middle of the sea.
So, it is quite a coincidence that the prime meridian that we use around the world has this property. The property of causing very little distortion when used to create the Peirce Quincuncial Projection.
Delving a little deeper, we see Greenwich chosen in 1884 and the Peirce Quincuncial Projection chosen in 1879. Just 5 years apart. That's interesting isn't it?...
I hope someone out there understands what I am trying to say. I have yet to get any feedback on this incredible coincidence and the fact that Wikipedia are showing the incorrectly calculated image.