Stall is threatened at all by all versions of garchomp, because skarmory can take half of its life and phaze it, which makes it really hard to wall it again, especially if it whirlwinds in something that forces it out. Now, you can predict the second SD, and i have. But that doesn't mean it's not threatening. And since when does rain stall run skarmory? Another reason that why would you ever run aqua tail over fire fang... unless you provide rain yourself. You now get ferro as a check, and you only beat skarmory and bronzong harder, and only if it's in rain. And if you need any kind of cred, i've used skarm basically since the start of BW.