It pretty much actually is that easy.
Just take a look at how the Soviets fought. Classic Zerg Rush. A good deal of the time, a significant number of soldiers going to battle didn't even have a gun, they had to loot it from fallen comrades. Granted, it wasn't only because the Soviets didn't have enough guns, but also because the Soviet officiers knew the fatalities would be so high that it ultimately mattered little if everyone or only every second one had a gun.
The problem is that that is exactly how they did
not fight when they started winning. David Glantz has identified several areas in which the Red Army steadily improved its capabilities, at higher strategic leadership and in small-unit tactics, in operational integration of combined arms, and in staffwork. There was no 'Zerg rush' about it; there has been nothing like 'Zerg rush' in actual military tactics since the nineteenth century. Successful Soviet operations required top-notch planning and performance like anywhere else in the war; when Soviet operations lacked this top-notch work, they often failed.
Glantz also tracked key improvements. Put loosely, they went something like this. From June 1941 to Septemberish 1942, even the Soviet varsity got squished by the Germans so long as the
Wehrmacht was properly prepared and had not reached culmination; only when German offensives were carried on into operational depth could the Red Army exert enough pressure to cause their halt. From September 1942 to June 1943, there was a sort of flux state, where the Red Army's best performed very unevenly (compare the success of Vasilevsky's attacks against the Stalingrad and Caucasus salient with the abject failure of Zhukov's Operation MARS at the same time) and still had problems with culmination (as at the Third Battle of Kharkov). From June 1943 onward, the Red Army's best was better than the
Wehrmacht's best, and the advantage only grew the following year when the Soviets annihilated Army Group Center.
Even then, the Soviet military lacked the capability to advance all along the front, because even the vaunted Russian steamroller wasn't big enough or logistically capable enough to do that. The
Stavka had to pick its spots, allocate resources at the best possible locations, husband troops and tanks for what was important, and integrate everything into an overall plan of operations and logistics. What changed between 1941 was not that the Russians got 'more' men or 'more' guns, bullets, tanks, planes, trucks, etc. What changed was that those resources were employed more carefully and skillfully compared to the wild haymakers that the Red Army launched in 1941 - attacks that only played into the
Wehrmacht's hands, even though they were powerful and desperate and mounted by soldiers who were as committed to their cause as any Red Army troops ever were.
This is the story with almost every story of military numerical superiority I can think of. It is not enough that an advantage exists: it must be used, and used properly. The American government possessed a vast numerical and industrial advantage over the slaveholding rebellion in the 1860s, but the US Army had to develop an advanced staff system and supply, and had to properly train and deploy its troops under able commanders, before that advantage told and resulted in victory. As with the Great Patriotic War, the final act of the American Civil War showed off that army's skills at its very best. The Manchurian Strategic Offensive Operation in August 1945 was a virtuoso display of operational maneuver, strategic redeployment, and more than a little hard fighting. (In true Soviet fashion, it also involved mass atrocities, most of which took place after the fighting.) And in March-April 1865, the Armies of the Potomac, Shenandoah, and James comprehensively annihilated the Army of Northern Virginia in the Appomattox campaign by outmarching and outfighting, a story of operational maneuver unlike anything else in the war in terms of how utterly the opponent was dominated by Federal forces that were always two steps ahead.
And conversely, in the Great War, there are countless examples of how the Entente badly squandered its vast superiority in numbers and machines: the Russians' many attempts at launching an offensive in Poland in 1914 and 1915, the Artois-Champagne campaigns in France, the whole prolonged nightmare on the Somme, the twin disasters of the Nivelle and Passchendaele offensives in 1917. Revolution tore Russia apart, sundered Ireland (and might have got more of Britain if not for the resumption of unrestricted submarine warfare), and after a fashion, showed up in France as well - each time, a result of not merely military errors but political errors. The Entente powers came perilously close to losing the entire war in March 1918, and if not for Ludendorff's poor operational decision-making they might very well have done so.
Taking a look at the pre-war industrial output, the Soviets and the USA alone were already possessing a much higher industrial capacity than Germany had when they were already all but on full war footing and that is before those nations went to go to war economy. Germany never even had enough resources to build enough weapons to even theoretically stand a chance, let alone actually produce all that, let alone crew all that equipment. Italy and Japan were the same picture, Japan in fact even worse as they already were on the verge of collapse due to a simple oil/gas embargo.
The retrospective of history is easy of course, but it doesn't change the fact that you could put a couple stasticians in a library with industrial and population growth data and they'd tell you the Axis would be insane to try a war and actually thinking they had any chance to win short of their enemies simply letting them without giving a fight.
And yet that doesn't work with the First World War.
Logistics, strategy, lack of counter strategy and on-the-field tactics are all force multipliers, yes. But you can only multiply whatever force you have so much until you hit your hard cap ... and that hard cap was so woefully lower for the Axis than it was to the Allies that their only hope was the Allies wouldn't even put up a fight. Which is exactly what happened in France and the early stage with the Soviets (one due to horrible planning, the other due to ignoring espionage reports). France together with the british Expeditionary Force had enough experienced troops to grind down the German offensive and the much famed strategical brilliance of going through the Ardennes is little more than pure luck. That troop train going throgh those forests wasn't the largest flanking manouvre of WW2, it was the largest traffic jam of WW2. Had any of the allied sentry forces down there noticed them, even the deployed third rate/reservist troops could have stalled all progress to such a crawl that reinforcements could have arrived early enough to turn the Ardennes into the world's biggest scrapyard.
It was pure luck that WW2 didn't end right then and there, same as it was pure luck that Stalin ignored a plethora of intelligence reports (the Soviets had bar none THE best espionage system on the entire world!) that were telling exactly what Germany was up to, including troop movement reports galore and everything someone in power would need only take ONE look at and see what's going on.
You reference a 'hard cap' to military potential, and claim that any statistician could have figured out that the Axis powers were screwed. The problem is that this 'hard cap' is an entirely imaginary number. It is anti-statistical. We don't know what the maximum potential for the German war machine was in the Second World War; we have guesses, but there is absolutely no statistical basis for claiming that the
Wehrmacht had no possibility of possessing the force multipliers to overcome its matériel deficit.
I agree that luck played a significant role in Germany's success in 1940, and luck undoubtedly aided the
Wehrmacht in 1941 as well. If anything, though, that just points up just how poor our predictive powers really are. By the numbers, by rights, the German army might well have lost in 1940 - but it got lucky, and
it took advantage of the luck it got, and its opponents contributed a fair share of mismanagement...so it won instead. Luck and good force multipliers clearly
can overcome a great deal of statistical inferiority. Fog and friction, as always, dwarf the efforts of soldiers and commanders to impose their will on the battlefield.
Look: I am not saying that Germany ought to have won the war, or that it was a shoo-in to win, or that the Allies themselves had to get very lucky to avoid defeat. None of those things is true. What I am saying is that the Allies could not simply crack open the champagne as soon as they heard Germany had invaded Poland in September 1939. It was not just that there were five and a half years of hard fighting ahead. It's that they had to learn how to fight the
right way. At the risk of being blindingly obvious, the armies that got annihilated by Germany in 1939, 1940, and 1941 were not trying to lose. They were, in fact, trying very hard to win, or at least (in the case of the French and British) to
not lose. Yet they were wiped out anyway. That they would eventually develop into tempered tools of war was not a foregone conclusion. But that development did happen. It's documented and everything. And it is inextricable from the eventual Allied victory.