...involves both frequency of occurrence and severity of outcome.
I totally agree that that risk involves both frequency of occurrence and severity of outcome. Which is why the frequency of 'severe' is over reported. I'll happily accept that moderate icing, minor windshear (+/- 5-10 kts), and moderate turbulence are occasionally encountered. What I'll not accept is "Previous aircraft reported severe turbulence/icing/windshear" and you follow two minutes later and find nothing of the sort. We also have to accept that different aircraft deal with these phenomena in different ways. I've descended in a turboprop at max. continuous power due to icing (I'd call that severe) yet jets in the same area powered up straight through the same conditions. I've landed on "icy" runways only to be asked by ATC about the braking action. They are are disappointed when you reply "Sorry, didn't use the brakes". So in my mind, when I hear the word "severe" is has the same value as the words "horrendous" or "crisis" - it is just a superlative because the reporter rarely understands its meaning. Too often the word "severe" can probably be substituted with "some". It is only when these reports have context will they have some real value.