As you already said, it's not perfect. The naval blockade that might be something with same effect is somewhat flawed on anything that the US or even Japan would have wanted. Giving time for the Soviets to come in could have just as likely made Japan want to never surrender under combined terms or be divided up. Blockade is murky next to an assured, decisive one. Like you said, take out the soviets, and the bomb and blockade become a non-issue.