I use the definition of overrated as; Thought of as most important by modern people, after the fact.
I am not sure whether I think (german) subs or strategic bombers are most overrated from the war. I will make a case for the bombers.
I also think the strategic bombers did little for the wareffort, at least when it comes in bombing of industry and population.
I think the net sum of moral for the nation being bombed is one of defiance, rather than dispair. Just look at reactions to 9/11, US was “never” more committed to fight the enemy, it united the nation, more than it caused a loss of moral.
the effect on industry is also negligable, at (I have only read about the germans). When russia took silesia in january 1945, it is estimated that it did a bigger damage for the total german war production (that is the production form jan-may 1945), than the all stratigic bombing of germany in WW2 combined.
When it comes to japan, the number for people that got killed is high, and they will be when you drop firebombs on houses made of paper. But most of the dead where civilians, it was also in the later part of the war.
the nuke is more difficult to assess, I know there is legitimate disagreement of whether the russian invasion of manchuria or the bombs or a combination was what made japan surrender.
HOWEVER, bombers have been very valuable after the war, and the dropping of the nukes was probably more valuable for the cold war than WW2.