Along just one front, they had 3700 aircraft, 80 subs and numerous other naval support. Could ally tanks have swum across to normandy? No, it's the same concept. They had 1.5 million ground troops which is far beyond the ability of japan to defend. Again this was just their northern front
They conquered manchuria in short order, in fact in between the two atomic bombs. The soviets then landed and captured the kuril islands attached to japan's main land, which remain in their control. Only then did japan surrender, a full month after the bombs
Stalin was never impressed by the bombs, which did very little damage to japan militarily. It did not impress much of japan's own high command either, as they attempted a coup on the emperor to prevent a surrender
Ok there is a lot to correct here.
1.
The Soviet military greatly exceeded the ability of the Kwantung Army, however it wasn't a pushover either. Most historians believe the Soviets massively underreported their casualties, especially in heavily engaged areas like Mudanjiang where the Soviet army was delayed and the Kwantung Army was able to extricate itself and began a withdrawal towards Korea. The Soviets place their casualties at a little over 10,000 for the entire Manchuria campaign, other historians estimate that 10,000 is a fair estimate for Mudanjiang alone. Either way the Soviets had, in point of fact, not destroyed the Imperial Japanese army which was able to extract the bulk of its major formations. When the Soviets attacked the Japanese were in the process of redeploying to Korea for a defense of the peninsula which is why they were caught strung out. However major formations had reached the Korean border and many more were en-route after the successful delaying action at Mudanjiang. The Japanese surrender in mid-August precluded further Soviet offensives and further engagements against a tenacious defender that still numbered several hundred thousand troops. Soviet victory was inevitable but it would have been paid for in blood.
What the invasion of Manchuria did however was obliterate the Japanese strategic map. Prior to the invasion Japan despite mounting losses held an apparently strong position in China. They had retreated to the coasts and tightened their lines of defense but they still dominated everything from Guangzhou to Beijing, they retained control of a strong puppet in Manchukuo, and their old dominion over Korea was unchallenged. This continental Empire gave Japan hope that it could drag out the war to such an extent that it might force favorable peace terms on the Allies, moreover it gave psychological confidence. The loss of islands and fleets was one thing, but the Empire was still relatively 'intact'. After the invasion it was clear that Japanese field armies and garrisons in China were unequivocally doomed and that nothing but the Home Islands could be defended.
That being said there is overwhelming evidence that the atomic bombings figured more prominently in forcing the immediate Japanese capitulation. It is incredibly unlikely that a swift unconditional Japanese surrender would have been forthcoming in mid August just because of the loss of Manchukuo-Manchuria and Korea. Devastating yes but it did not directly imperil the Home Islands nor did it deflect from the possibility of a terrible resistance that might minimize the peace conditions. With the atomic bombings it completed the strategic picture of total and utter defeat.
2.
The invasion of the Kurile Islands took place after Japan had officially broadcast its surrender. As a result the garrison troops mounted only a haphazard defense with some choosing to observe the ceasefire and others resisting. Nevertheless the Soviets still suffered heavy losses from this sporadic resistance. It was the attack on Sakhalin which occurred before the surrender and that island was lightly defended but it still strained the capabilities of Russian sealift. There is not evidence that the Japanese greatly feared an assault on the home islands from the Soviet Union. The Soviet sealift was only possible as the result of major United States shipping transfers under Project Hula which saw close to 4,000 vessels transferred into Soviet service. Nevertheless it is unlikely in the extreme that a Soviet landing on a major island like Hokkaido could have been successful.
3.
Incorrect. The Japanese 'high command' did not launch a coup (nor was it launched against the Emperor, that would have been sacrilege), it was instead a desperate attempt by a fanatical major named Kenji Hatanaka who attempted to stage a palace coup utilizing a few hundred troops and counterfeit orders. It failed but it does demonstrate that Japanese troops were willing to engage in fanatical resistance even in the aftermath of major defeats and the atomic bombings.