I find it is important to be skeptical of people's descriptions of what they were supposedly thinking years earlier. Much better is to find contemporaneous accounts. For example:

>...my grave misgivings, first on the basis of my belief that Japan was already defeated and that dropping the bomb was completely unnecessary,

The last major battle before the dropping of the atomic bombs was the battle for Okinawa and it was the bloodiest and fiercest battle fought against the Japanese. Absolutely no one who knew about that battle would have claimed that Japan was already defeated.

>...When the guns fell silent, more than 240,000 people had lost their lives in the campaign for Okinawa. The American loss rate was 35 percent of the force, totaling 49,151 casualties.

>...So close to the home islands, most Japanese soldiers refused to surrender and fought to the death. Their fanaticism contributed to a dreadful toll. Some 110,000 Japanese and conscripted Okinawan defenders were killed in action.

https://www.nationalww2museum.org/war/articles/okinawa-costs...