So I spoke with Brightleaf a bit about the whole simming Mastery>Haste but how most top end Ele shamans still reforging Haste>Mastery.
Basically, problem is the stats become skewed when you reforge all the way to mastery, leaving such a low amount of haste that all of a sudden the sim thinks haste is a lot better. It's been that way for quite awhile. You have to have a balance between the two and reforging Haste>Mastery at our gear levels gives us the perfect balance of not having Lava Burst cast time go below GCD and still give us a good amount of mastery, 40%+. Balance has been shown to be favored, basically.