We analyze healers a lot differently than other sources - we built a healing simulator to be able to handle all of the complicated variables that go into healing. Gust of Mists is being calculated correctly in the simulator and in our gearing strategies.
Right now if I look at the gearing strategies on the site - mastery isn’t weighted very high for a raid healing strategy with refreshing jade wind. It is ranked as pretty good for some other talent builds, and especially in mythic+. That is a logical result - the more spot healing you do, the more valuable it will be.
Looking at healing parses is pretty misleading - it is very easy to “game” those. And, usually the high parses are raids in which that healer was able to completely ignore spot healing and almost completely focus on AoE healing. Most healers/raid teams don’t work like that. You have to be more of a “jack of all trades” and throw out a few more vivify or an enveloping mist or two. The amount of movement you have to do will heavily affect mastery as well, since you won’t be able to get as many soothing mist ticks in. Right now the gearing strategies assume you are very efficient with your movement. I do plan to add some more movement into the healing gearing strategies sometime soon, but I think what we have now will work well.
I don’t know how other guide sources are determining the values for the different stats, but I do know that we are the only ones doing simulation - which means we are taking into account a lot more factors than any other source of information.
I’d say: before you assume the advice won’t work - try it out. If you find yourself getting very few gust of mist procs, then, you’ll want to adjust your stats or adjust your play so that you get more of them.