Note that there was a third bomb scheduled and in preparation and it was decommissioned and returned to Los Alamos.
Also note that the conventional bombing of Tokyo just a few months prior caused greater destruction and loss of life.
Evaluations have to be made in context, which is very hard. There was a lot of anger and pain on both sides, which lead to irrational "momentum" in prosecution of war. Also there is the logic of industrial warfare: look at Europe: many smaller German cities were bombed for the first time just in the the last month of that war, because a huge machine had been switched on that just kept emitting planeloads of bombs which had to be dropped somewhere.
There is a thoughtful discussion of this topic by Tooze from just a few days ago: https://adamtooze.substack.com/p/chartbook-230-burning-hambu...