To the people on the ground, the fact that an A-bomb could be dropped from just one bomber made no difference. Fire bombing or A-bombing was roughly the same to them. Indeed, fire bombing was probably worse when it came in waves.

There were no medium or large cities left to flatten in August 1946.

I've read before, and I believe, that the Japanese military leaders and emperor were not that impressed with the A-bomb. And why should they have been? They already were ready for a one-condition surrender, and the U.S. did accept it (calling it unconditional, but the U.S. adhered to the one condition).