When you have the fact that the Japanese had already sent delegations to negotiate a surrender, that everyone who wrote at the time either knew that Japan was t

When you have the fact that the Japanese had already sent delegations to negotiate a surrender, that everyone who wrote at the time either knew that Japan was trying to surrender or was confident that they would surrender as soon as Russia entered, and that the US Strategic Bombing Survey also concluded that the bombs were unnecessary, we're getting outside the realm of your standard counter-factual here. It's much more like saying 'well, this body was stabbed through the heart and then burned, but they almost certainly would have been dead even without the burning' than 'some complex series of actions occurred and we have no idea which of them was actually relevant in the resulting outcome'.