The European wire gauge system makes no sense. There I said it. I don’t need to know the O.D. of the wire, I need to know the amp rating. The O.D. only becomes an issue for bending radius and there is a chart for that as well. Nothing is stopping some a**hole from making a wire almost completely out of plastic that has the O.D. of a typical 14AWG but can’t carry any serious amount of current under the European system. Under the AWG you always know what the current capacity is.
And while we are at it, you might as well standardize your wire sizes based on copper. You are never going to use anything except copper. So your units should reflect the material. I am building a chemical skid, that has nothing to do with the distance between the equator to the north pole.
Also when is the last time you were running wires that you needed a mm of precision? Meanwhile a fraction of an amp really does matter. So should not the thing that does matter be reflected in the product?