This is absolutely true.

All these leaders:

- Adm. William Leahy (President Truman’s Chief of Staff)

- Henry Arnold (US Army Air Forces commanding general)

- Adm. Chester Nimitz (Commander in Chief of the Pacific Fleet)

- Maj. Gen. Curtis LeMay, (head Bomber Command)

- Gen. Dwight Eisenhower

are all on record as acknowledging that "Japan was already defeated". [1]

[2] Japan knew they could not win and were concentrating on obtaining the best possible terms of surrender, hoping that Stalin might be convinced to mediate a settlement between the United States and Japan. This hope was dashed by the Soviet declaration of war and invasion of Manchuria and Sakhalin Island, which happened at 1 minute past midnight on August 9, 1945 [3].

Another important factor is that Japan had good reason to be wary of USSR military might [4]. It's arguable that Japan's fear of fighting the USSR is the reason Japan went east (to Pearl Harbour) instead of west (to eurasia) in Dec. 1941 [5].

[2] and [5] are thoroughly researched and make compelling arguments.

[1] https://www.thenation.com/article/why-the-us-really-bombed-h...

[2] https://foreignpolicy.com/2013/05/30/the-bomb-didnt-beat-jap...

[3] https://en.wikipedia.org/wiki/Soviet%E2%80%93Japanese_War

[4] https://www.warhistoryonline.com/war-articles/effects-nomonh...

[5] https://www.amazon.com/Nomonhan-1939-Armys-Victory-Shaped/dp...

There's a good book on the topic if you want more:

https://www.amazon.com/Nomonhan-1939-Armys-Victory-Shaped-eb...