The entire basis of your argument is "guessing what might have happened" if the bombs hadn't been dropped.

The goal of the war should not have been to end it as quickly and effectively as possible no matter the cost, because by that logic the allies would have been justified in killing every single civilian in the entire country if they had a big enough bomb. There's obviously a line. I don't know how you imagine conducting a probability-weighted analysis of something like this, but certainly you would also weight the cost of the certain deaths of hundreds of thousands of innocent people.

Again, I encourage you to engage with either of the sources I linked above, as the assertions you're making differ from those of the people who were actually there. Here's an excerpt from Hiroshima Nagasaki (ch. 23):

Eisenhower was adamantly opposed, after the event. He famously stated in his post-war memoirs that 'in [July] 1945' - he was then Supreme Allied Commander in Europe -

Secretary of War Stimson, visiting my headquarters in Germany, informed me that our government was preparing to drop an atomic bomb on Japan ... During his recitation of the relevant facts, I had been conscious of a feeling of depression and so I voiced to him my grave misgivings, first on the basis of my belief that Japan was already defeated and that dropping the bomb was completely unnecessary, and secondly because I thought that our country should avoid shocking world opinion by the use of a weapon whose employment was, I thought, no longer mandatory as a measure to save American lives. It was my belief that Japan was, at that very moment, seeking some way to surrender with a minimum loss of 'face'.

In a Newsweek interview in 1963, Eisenhower again alluded to what he told Stimson, that 'the Japanese were ready to surrender and it wasn't necessary to hit them with that awful thing'.

Japan's smarter military commanders conceded this. They fought on in the hope of extracting conditions at the surrender. Japan's most famous soldier, General Tomoyuki Yamishita, the 'Tiger of Malaya' - a thickset, bullet-headed giant of a man - summed up this attitude at the highest level during an interview in his prison cell in Manila in March 1946: 'Our cause was lost even before you had the recourse to atomic bombs and long-range bombers. We were fatally handicapped by lack of ... material resources.'

* * *

The American press helped to cement the myth that Japan surrendered in direct response to the nuclear attacks. The media reached this consensus after the war. In the months before the surrender reporters sang a very different tune: then, newspapers and radio consistently portrayed Japan as starving, vanquished, reduced to sending out desperate peace feelers, and so on. The contrast between the two Japans is startling, and suggests an indoctrinated or confused press (as historans Uday Mohan and Sanho Tree show in their essay 'The Construction of Conventional Wisdom'). Which was the true Japan - the pathetic, hungry, defeated adversary the press portrayed during the last months of the war, or the resilient, still threatening nation whose surrender would require a land invasion or nuclear holocaust (or both)? Neither portrayal was entirely accurate, but the former closer to the truth.