>I think it's pretty clear ...

I don't think there is a clear consensus on any of the points you bring up:

>...a) the Japanese had been willing to surrender on one condition (keeping the emperor) for weeks,

https://en.wikipedia.org/wiki/Surrender_of_Japan

>...On June 9, the Emperor's confidant Marquis Kōichi Kido wrote a "Draft Plan for Controlling the Crisis Situation," warning that by the end of the year Japan's ability to wage modern war would be extinguished and the government would be unable to contain civil unrest.

>...Kido's proposal did not contemplate Allied occupation of Japan, prosecution of war criminals or substantial change in Japan's system of government, nor did Kido suggest that Japan might be willing to consider relinquishing territories acquired prior to 1937 including Formosa, Karafuto, Korea, the formerly German islands in the Pacific and even Manchukuo.

In July, Togo told the ambassador to the Soviet Union:

>...Although the directing powers, and the government as well, are convinced that our war strength still can deliver considerable blows to the enemy, we are unable to feel absolutely secure peace of mind ... Please bear particularly in mind, however, that we are not seeking the Russians' mediation for anything like an unconditional surrender.

>In reply, Satō clarified:

>It goes without saying that in my earlier message calling for unconditional surrender or closely equivalent terms, I made an exception of the question of preserving [the imperial family].[49]

>On July 21, speaking in the name of the cabinet, Tōgō repeated:
With regard to unconditional surrender we are unable to consent to it under any circumstances whatever. ...

>...b) the U.S. was holding out for an unconditional surrender

It is more accurate to say they were holding out an acceptance of the Potsdam Declaration.

>...c) the USSR entering the war pushed Japan to make, and the U.S. to accept, a privately-conditional / publicly-unconditional surrender.

It is not like the US didn't know the Soviet Union was going to enter the war. When the Japanese government demanded that the emperor would remain in power, the reply simply was:

>...From the moment of surrender the authority of the Emperor and the Japanese government to rule the state shall be subject to the Supreme Commander of the Allied powers who will take such steps as he deems proper to effectuate the surrender terms. ... The ultimate form of government of Japan shall, in accordance with the Potsdam Declaration, be established by the freely expressed will of the Japanese people.

Eventually Japan agreed to the Potsdam Declaration.

>...From a Japanese perspective they destroyed nothing that hadn't already been firebombed to smithereens

That is basically true and had been true for months. The question is why did so many have to die in Okinawa? I think an argument can be made that the atomic bomb made it very clear to the emperor how ruinous the situation was and pointing at the bomb allowed him to save face:

>...In a meeting with the Emperor, Yonai spoke of his concerns about growing civil unrest:

>I think the term is inappropriate, but the atomic bombs and the Soviet entry into the war are, in a sense, divine gifts. This way we don't have to say that we have quit the war because of domestic circumstances.

Indeed the major reason that Hirohito publicly mentioned in his speech to the nation was:

>...Moreover, the enemy has begun to employ a new and most cruel bomb, the power of which to do damage is, indeed, incalculable, taking the toll of many innocent lives. Should we continue to fight, not only would it result in an ultimate collapse and obliteration of the Japanese nation, but also it would lead to the total extinction of human civilization.

https://en.wikipedia.org/wiki/Jewel_Voice_Broadcast

>...It's really hard to believe that the war with Japan would have had a different outcome if either or both bombs had not been dropped.

There is no way that Japan would have "won" the war at point, but if the surrender of Japan had been delayed and the invasion occurred, there would have been many more casualties on both sides. Both sides were preparing for a horrific battle:

>...Instead, everything was staked on the beachhead; more than 3,000 kamikazes would be sent to attack the amphibious transports before troops and cargo were disembarked on the beach.[8]
If this did not drive the Allies away, they planned to send another 3,500 kamikazes along with 5,000 Shin'yō suicide motorboats and the remaining destroyers and submarines—"the last of the Navy's operating fleet"—to the beach.

On the other side:

>...Operation Olympic, the invasion of Kyūshū, was to begin on "X-Day", which was scheduled for 1 November 1945. The combined Allied naval armada would have been the largest ever assembled, including 42 aircraft carriers, 24 battleships, and 400 destroyers and destroyer escorts. Fourteen U.S. "division-equivalents" (13 divisions and two regimental combat teams)[28] were scheduled to take part in the initial landings.

and if that armada wasn't enough:

>...Ken Nichols, the District Engineer of the Manhattan Engineer District, wrote that at the beginning of August 1945, "[p]lanning for the invasion of the main Japanese home islands had reached its final stages, and if the landings actually took place, we might supply about fifteen atomic bombs to support the troops.

https://en.wikipedia.org/wiki/Operation_Downfall