the brave USAians decided their last option was to level two large cities in Japan.. ?

There's a fine line between bravery and stupidity. The immediate psychological impact of the atomic bombs crippled the Japanese in a way that no amount of fire-bombing or land attacks could have. The Japanese Navy was indeed out of the picture, but Japan was not ready to surrender, and the loss of Japanese life from the two A-bombs was nowhere near what it would have been with continued firebombing.

I'm curious as to what your ideal end to the fighting in the Pacific Theater would have been... More loss of life from firebombing? A Japanese victory?