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But you don't have priority when Cavern of Souls enters the battlefield. In the very least, your opponent can just float the mana until the end of whatever phase it is, and only an idiot would drop Cavern against you with a Ghost Quarter out, then pass priority without casting something.
Besides. What you described takes 3 cards to deal with 1. And that's just for one Cavern of Souls . Having one-sixth of your deck a counterspells in today's meta is just silly.