I look at it this way: Tauros can throw out CB Returns however it likes. Then two things can end up happening: A) It gets wise to your Metagross switch-ins and throws out an Earthquake. B) You try to predict that Tauros predicts you and try to switch to Gyarados. When the latter option is available and fails you, then that creates a problem, as losing one single pokemon can put a serious hole into your overall defenses. You shouldn't have to rely both on one Pokemon AND your opponent at the same time to keep an opposing Pokemon at bay. I've always believed in having some sort of backup/exit strategy when it comes to covering your weaknesses. Also note Explosion on Metagross. It's likely that Metagross can die before the CBer is done rampaging.