Please compare and contrast the atomic bombing of two cities, and the incendiary bombing of over two dozen cities. Do you see any moral distinction between, let us say, the atomic bombing of Hiroshima and the incendiary bombing of Tokyo?
Compare the death toll and damage from conventional and fire bombs dropped on Germany to that of the final 2 atomic bombs dropped on Japan
One possible moral distinction: even in WWII, when the precision targeting technology just wasn't there, in some cases, ordinary incendiary bombs could be reasonably directed toward enemy troops or assets. You can see this in the early period of the War in Europe, when the US Army Air Corps did daytime bombings focusing on Nazi military assets. This was in contrast to the RAF, which did nighttime carpet bombings of whole cities, city block by city block.
Even if they predictably caused a whole lot of collateral civilian damage, the USAAC was justified in using incendiary bombs targeted "as exactly as they could" ---these bombings, though devstating, were not targeting the civilian per se.
I don't know whether the bombings of e.g. Tokyo were intended to slaughter and incinerate civilians, or if they were focused on military assets but (collaterally) resulted in horrific city-consuming firestorms. If they were solely intended to destroy military assets, they were justified. If they were not --- if they were intentionally focused on civilians, or deliberately indiscriminate --- they were the moral equivalent of Auschwitz, the London Blitz, or Planned Parenthood.