Even if what you say is true,
we had no way of knowing it. No effort was made, say, though diplomatic channels, to apprise us of this. If I had been in Truman's place in 1945, knowing what he knew then, I would have done the same thing he did. If I was in his place knowing what I know now, I still would have probably done the same thing. I would have had no guarantee that what I knew would predict my future. Neither did he have any guarantee those planes would get through, or that either or both of those bombs would actually work.
In my opinion, his action was the only option.