The issue was patience: Americans were running out of it. Already there was resistance by soldiers who had fought in Europe to transfer, and as Stephen Ambrose noted in his "Band of Brothers," at the end, based on the medal and point system, men who had never been interested in medals suddenly thought about them a lot.
Without question, the bomb saved an enormous amount of lives---ours, but some Japanese too. But the final outcome was not in doubt after Leyte, or, perhaps, Midway.
BTW, I address the whole Strategic Bombing Survey in "America's Victories: Why Americans Win Wars . . ." and largely the analysts were far too narrow in their investigation. They asked, "Did the bombing stop German war production?" No, it increased. But what they missed was that the bombers themselves acted like giant roach motels, sucking up the Luftwaffe into air combat (later, un-winnable air combat due to long-range fighter escorts) that "attrited" the Luftwaffe down to nothing. Some 30% of German WAR PRODUCTION was directed at anti-bombing in the WEST, a fact that by itself means that the Battle of Kursk easily could have gone to the Germans without our bombers hundreds of miles away. The Strategic Bombing analysts were looking for evidence we destroyed the Luftwaffe on the ground. Their eyes were too low: we destroyed it in the air.