The V1 was a serious nuisance, but too erratic to be a war-winner. Given the Allies' air-superiority, stripped-down chase-planes could intercept them, and prox-fused AAA culled many more...
V2 was not going to be cost-effective without CBW or nuclear warheads. The former didn't happen due the prospect of reprisals in kind against Berlin etc. The latter was improbable because they began late, after they'd managed to exile, alienate or imprison most of the scientists they needed. IIRC, too few 'senior' physicists stayed to be able to correct their comrades' theoretical errors. IIRC, building the V2 killed more 'slave labour' than the civilians it fell on...
I'll NOT venture into 'BELL' country because #1, given the multiple strata of 'urban legend' intercalated by oft-wild conspiracy theories, I do not know what it really was, and #2, I've a suspicion it might have been a clunky 'Calutron' aka Electro Magnetic Isotope Separation (EMIS.) "EMIS enrichment is an inefficient process: It would cost $81,000 to enrich a single pound of uranium". IIRC, the Manhattan Project used such for 'Proof of Principle', then went to 'gas diffusion', which was scalable...
IMHO, building a few 'super tanks' was a bad, bad move. Building too few was worse. Building otherwise nice tanks with overlapping road-wheels that made minor field repairs hideously difficult was seriously stupid.
IIRC, although some early jet-engines were *cheap* compared to piston engines, they had a very short life plus a distressing habit of shedding blades. The robust versions needed high-temperature alloys which were in very short supply...
Let's not go near the ME 163 with its infamous, pilot-eating T & S Stuff...
IMHO, the biggest blunder among the Vs was the V3. It didn't work, it swallowed vast resource, it diverted precious tooling and 'slave labour', and the site was unable to re-locate when the heavy bombers came hunting. Urban legend holds that, post-Normandy, when De Gaulle reckoned the captured site *could* be cleaned up and made to work, Churchill sent Sappers to collapse the hill...
Biggest blunder of all ? Surely, the Holocaust. Not only was it a ghastly, unspeakable waste of people but, IIRC, it was given rail and materiel priority over Eastern Front logistics...
Exterminate harmless civilians rather than supply an existential battle-front ??
Yeah, right...