[themaninthedark]

If the argument is that "We can't say that the atomic bombs were the catalyst for Japan surrendering because the surrender happened after a bombing and Soviet war declaration therefor they are confounding factors" then the same holds true for the argument that the Soviet invasion was the catalyst for surrender.

Now I will say that I have not read Hasegawa's book but Wikipedia says that it is "challenging the widely accepted orthodox view that the atomic bombings on Hiroshima and Nagasaki were the most decisive factor in Japan's decision to surrender ending the war against Japan."

It will be interesting to read but it looks like that it is not the accepted theory and that primary sources from the era were destroyed on all sides.