You are not wrong. While Ideal makes great wire nuts, I have to agree those graphs are just junk. It's not really information that lends itself to a bar graph.
This document is available for US models and gives you the exact info you need:
Other brands have similar reference materials. Here is the section for the US equivalent, model 76B:
That's more like it, right? But it's a lot to put on a label.
The picture in the question is a Canadian version of the wire nut (or would that be a marrette?) and I can't find an equivalent document for their Canadian product numbers. Ideal's web site was updated a while ago and is half useless.