The Western snaffle bit she used as an example got a 23 because of the broken mouth and the shank length. I rated the bits in my dressage double bridle using her article. Still mild but near the high end of the range. It rates a 1. To make a long story short, snaffles aren't always the mildest bit.
Severity depends on LOTS of things.
They were surprised at how much stronger the bit seemed compared to the way her horses responded to a regular eggbutt snaffle. Here's the method so you can apply it yourself, if you need to. The article is long and complicated because it considered both curbs and snaffles in the same rating scheme. Answer the questions and write down the point value indicated. At the end of the questions, I rated her bit as an example.