His assessment might have been more accurate without the A-bombs.
It's not the same as Churchill's position in 1940. If the Germans had invaded and overrun Britain he was resolved to move the government and as much of the army as he could get out to Canada. But, he had the prospect of eventually building a coalition with the U.S. and using the Dominions to build up the strength to go back. The Japanese couldn't have done that. Their navy is destroyed and cannot be rebuilt in China, so if they did not surrender they would not see Japan again.