I'm accepting the premise of the Allied powers including the Soviet Union.

This is nonsense when the SU was deliberately cut out of the deal anyway. Obviously the SU didn't want a Japan that didn't go through a de-fashifying process, but that's mostly what they got with the American occupation, which is how we got the modern liberal state that literally worships its fascist forebears and maintains an ethnonationalist ideology. I'm sure you don't need me to tell you about Unit 731 getting off scot-free or the rest of it.

Then, the Soviet Union declared war on Japan roughly around the time that the bombs were dropped.

This was not entirely a coincidence. Again, you are completely ignoring the significant "sticking it to the Reds" angle. A fantasy US that actually cared about sparing lives would allow the Soviet Union to begin its invasion to it and the SU can negotiate for conditional surrender that keeps the Emperor from a still-stronger position.

I don't know how to explain to you that the US was a deeply racist state that held Japanese lives to be subhuman to the point that they fully were non-factors in proceedings other than as a vector of attack to twist Japan's arm. See the Korean and Vietnam wars were there was also extensive reporting on the dehumanization of "g**ks" done by all facets of society, civilian and military.

By the time there was only one condition, an atomic bomb had been dropped.

Remind me, how strongly connected were these two events? Right at the end, as you have somewhat noted, many things were happening at once.

The most generous interpretation, which I don't uphold, still neglects that there was not only one bomb dropped and the second one has remained without even a gesture at justification.