The goal of the graph and cross sections is to help demonstrate the relative warmth of the various models. I shy away from temperature ratings because it is so subjective to each person's physiology. I have cold hands. And I know that. So for conditions that may only require an M1 Pro glove for some (like riding chairlifts on a cold, windy day in the 20s), I'm probably putting on the M1 Mitten. However, it can be 5 degrees, but if I'm working hard and breaking trail on a skin track an uninsulated glove like the TOUR will be perfectly fine. It helps to identify 'your' temperature rating and the conditions you plan to use the hand wear in most often. Let your past experience and intended use help drive the decision when it comes to what will be most suitable for the next purchase.
Graph of relative warmth based on insulation package AND design. Mittens generally occupy a higher tier simply because your fingers share the same space which inherently makes them a warmer form of hand wear.
Note that gloves at the bottom tiers are uninsulated but still have a relative position based on materials. For instance the full leather construction of the M4 makes it warmer than the lighter weight/breathable textile of a bike glove.
Insulation Cross Sections
(In order of relative warmth based on insulation AND design)