Honestly, Round isn't a very good choice either. You'd probably see a significant damage improvement if you switched to Return/Body Slam and focused the EVs more into Attack. And Power Whip would hit Tyranitar much harder either way, as well as dealing with Politoed and other Water-types.
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RNG is kind of like firing a gun. Why shoot blindly in every direction until you're lucky enough to hit the target when you can just take the time to aim properly and hit it with one shot?