I don't want to start a war over this but from what I have read it wouldn't no wonder weapon would have ever made a single bit of difference to the outcome of the war.
By the end of the war America's economic output was around 50% greater than ALL of Europe combined - that's Britain, Germany, occupied Europe, European Russia, the works. Once the US mill starts to grind there is no stopping it.
I was trawling the web the other day and found a link about US Carriers. It seems that the US built over one HUNDRED fleet carriers (that's escort carriers, light carriers and attack carriers) by the end of 1945, and that doesn't include all the jeep carriers and aircraft tenders it made ! The Japanese made around 30 of all marks (mostly cheap conversions) if I remember. No contest.
And even though Americans (quite rightly) hate getting into long drawn out wars, when they DO decide to fight it is all or nothing - Unconditional Surrender since 1865 !
So even if the Japanese or Germans had developed their wonder weapons, smashed the Allies on D-Day or nuked New York it wouldn't have made a diference - in Total War America could never be (and still can't be ) defeated.
Quelling armed insurgencies and ending low level conflicts - not so good. But then - who IS good at that ?
Roni