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I'm not sure why you're using a z-test when you can calculate the probability directly. The chance of landing 22 or fewer Hurricanes out of 46, given that the true probability of landing one is 0.7, is approximately 0.00136, or 0.136%. You're off by a bit more than a factor of two...
But if you Snatch a Shell Break, Cloyster will still be dead on the next turn, except you have a massive boost.
That being said, it's still highly situational to be virtually ineffective.
I can see it being useful if you know you're faster than a sweeper who has accumulated, say, two Swords Dances, and you need a guaranteed revenge kill.
You might also want to give the expected BP by weighting the damage with the probabilities.
It's just under 85 for non-skill link, for those interested.