>you can get the same "nuke" mushroom clouds with big swags of TNT detonations, so maybe nuke tests were faked
Exactly. Also, how do you get a fireball from a nuke? Some pics and videos don't show a fireball but some do. Uranium or plutonium don't combust.
>Nagasaki and Hiroshima were probably massive firebombings like Dresden in WW2
Definitely a fire-bombing. Many buildings and even trees were left intact. The houses were all made of wood so they burned up easily.