Is it a fair assessment (in hindsight) that Japan feared the USSR more than US atomic bombs?

[Dissonance]

@davidmich

Was Japan going to surrender anyway prior to the atomic bombing of Hiroshima and Nagasaki? More modern research suggests it was.

No there isn’t. The US was reading in real time all of Japan’s diplomatic radio traffic which Japan thought was coded in an unbreakable cypher. From Richard B. Frank’s Downfall: The End of the Imperial Japanese Empire

The most often repeated condemnation of American diplomacy in the summer of 1945 is that policy makers understood that a promise to retain the Imperial institution was essential to end the war, and that had the United states communicated such a promise, the Suzuki cabinet would likely have promptly surrendered. The answer to this assertion is enshrined in black and white in the July 22 edition of the Magic Diplomatic Summary. There, American policy makers could read for themselves that Ambassador Sato had advised Foreign Minister Togo that the best terms Japan could hope to secure were unconditional surrender, modified only to the extent that the Imperial institution could be retained. Presented by his own ambassador with this offer, Togo expressly rejected it.

All three military members of the Supreme Council for the Direction of the War remained opposed to surrender even after both bombs had been dropped and the Soviet Union entered the war. It was only Emperor Hirohito’s personal appearance at the council indicating his wish to surrender that caused the military to cave and accept surrender.

@RealityChuck

The Japanese were already seriously considering surrender before Hiroshima. They indicated it to the allies, but a mistranslation (probably deliberate on the part of a Soviet agent in the German embassy) led the US to believe they had rejected the idea.

Not this old chestnut again. I assume you are referring to the Japanese response to the Potsdam Declaration being "mokusatsu" and that it was mistranslated to be a rejection when the supposed intent was more akin to “we’ll think about it.” This is untrue,

Mokusatsu (黙殺?) is a Japanese noun literally meaning “kill” with “silence”, and is used with a verb marker idiomatically to mean “ignore”, “take no notice of” or “treat with silent contempt”.[1][2][3][4][5] It is composed of two kanji characters: 黙 (moku “silence”) and 殺 (satsu “killing”).

In other words, Japan’s official position on the Potsdam Declaration translated in the best possible light was that they were going to ignore it. The Potsdam Declaration was an ultimatum demanding the unconditional surrender of Japan:

“We call upon the government of Japan to proclaim now the unconditional surrender of all Japanese armed forces, and to provide proper and adequate assurances of their good faith in such action. The alternative for Japan is prompt and utter destruction.”

Announcing that one intends to ignore an ultimatum is a rejection of it.