I'm not sure what in my comment you're specifically referring to, but...sure, I'll bite.

Let's split hairs. The Tokyo firebombings killed, per Wikipedia, 80K-130K civilians, depending on your estimate. Again per Wikipedia, Little Boy killed 70K-126K civilians, as well as an additional 7K-20K soldiers and 12 American POWs. Given those numbers, rather than "more deadly" I'd prefer to say "just as deadly".

You're far from the only one in this comment thread to do this, but...I don't understand why the fact that the firebombing of Tokyo was approximately just as deadly as Hiroshima is supposed to somehow absolve Hiroshima. Most people who think Hiroshima was a war crime also think Tokyo was a war crime. The way I prefer to approach moral analysis, personally, isn't especially utilitarian - once we start splitting hairs about which war crime was more or less moral I can't help but feel like we might've lost the plot.

Now, with that aside, we can play some games here. Tokyo was (and is) a city an order of magnitude bigger than Hiroshima; 100,000 dead in Tokyo vs. 100,000 dead in Hiroshima means, in a sense, the attack on Tokyo was an order of magnitude less vicious. Maybe "viciousness" of an attack isn't especially meaningful on its own - if the US bombed the middle of nowhere to make a point and only a handful of people died it definitely wouldn't be as evil, even if the strength of the attack was the same. But this did have practical consequences - the infrastructure of Hiroshima to deal with the situation was demolished utterly. This meant no health care or support for any survivors - supposedly exactly one doctor was left uninjured. People were just left to suffer for days. In Tokyo there was still some health care available, there were still some support networks; because the destruction - awful as it was - was so much less complete, there was a much better chance that survivors could lean on friends or family for support. So the suffering of the survivors in Hiroshima was much greater. In this awful utilitarian Olympics of evil, the atom bomb takes a point.

There is, of course, the issue of radiation sickness. We do intuitively feel that, regardless of the particular numbers involved, chemical or biological warfare is a red line that musn't be crossed. It's one thing to blow people up, it's another thing to poison them - or give children cancer, as the case may be. Truman himself felt that way - although the scientists at Los Alamos had some idea about radiation Truman didn't, and some believe he might not have approved using the atom bomb if he'd known [0]. In that light, Hiroshima was definitively less moral than the firebombings.

And I guess it's worth stating that the truly deadly firebombing of Tokyo, Operation Meetinghouse, didn't come out of nowhere. The US had been bombing Japanese cities for three years. Operation Meetinghouse wasn't a surprise; it wasn't the first bombing of a Japanese city, it wasn't the first firebombing (that was in Kobe), it wasn't even the first firebombing of Tokyo (which happened a month prior). Since my argument here has been primarily "the US should have given the Japanese an understanding of their capabilities and given them an opportunity to surrender in light of them", I think you can make the case that they had with Tokyo in a way that they hadn't with Hiroshima, and that - at least by my own standards - that makes Hiroshima far more morally problematic.

[0] https://blog.nuclearsecrecy.com/2012/10/18/who-knew-about-ra...