Their destructive power is just advertising. The Allies aerial firebombing campaigns against Japan and Germany were vastly more destructive than the supposed atomic bombs allegedly used against Japan by the US; by the numbers, from the US own accounts of the events. Supposing that atomic bombs were actually used against Japan, the demonstrated effects of the atomic bombs were highly inconsistent with the predicted (advertised) effects perpetuated by its creators and proponents. They certainly didn't destroy the entire cities, nor kill most of those cities populaces, nor render the cities uninhabitable from radiation, and On and on.

Your first clue that something's rotten: why don't 'we know' how devastating these nuclear weapons are? How is it that these nuclear weapons we're constantly told exist, and are simultaneously (and paradoxically) told are both unquestioningly necessary and an existential threat have never been used...by any nation possessing them? None. Not even once. Does it really sound plausible that the worlds military forces suddenly came to practice self-restraint? Is there any evidence that military's devote incredible amounts of their budgets to manufacturing their apex weapons in order not to use them? History shows the opposite to be true, every time. Every time. "But not this time, this time something's different." Nothing is different. If they were real they would be used.