I am not denying that, I just think that especially for the WW2 era it is totally useless (excluding the Western democracies).Of course I don't think GDP is an all embracing measure of warmaking potential but it's a good measure of the economic size and per capita figures, of the level of development of a country.
It is just that the very nature of GDP (and the data involved) calculations can be regarded as a very unprecise process.The numbers for all instransparent systems are simply bollocks. Even the figure of the USSR aid by just 5-10% is nonsense (only a naive economist or leftist anglophobic economist like Harrison could believe in such garbage), if I had to make a good guess, I assume that it was much higher (of total share), one of the major reason between the difference of collapse and non-collapse during both world wars, but most people consider such statements to be offensive.
I would argue that the aid France received during WW1 was actually smaller.
Another interesting difference was the manpower pool, while Hitler caused the effective destruction of a European defense against Bolshevism and fought the war alone, while also enabling an Anglo-Saxon- Soviet alliance (which is hilarious bringing them to the table, diplomacy is another factor). It is one of the reasons Putin is waging a war in Ukraine: It is not only the fact that he wants to make it uninteresting for the EU, grab resources or prevent it to become democratic, but as Brzezinski stated: "Russia is not great without Ukraine". He needs the manpower and with it, access to the Danube and Crimea (making a bridge from Kerch obsolete).
So, It is better to look at the direct focus on conducting war and the war industry (intentions = actual vs capacity = theoretical).
There are no comparable goods for an exact calculation.
There are also countries which live above their standards, a further distortion.
In the end, Germanies values would be probably around 2,500 post war while nowdays it would be around 3,203 (this would be fairly close to 90-015 figures).
The USSRs range of 500-1,700 is probably more realistic (for the pure "economy" part that is), your figure of 9,274 is totally dubious. You want to tell me that the USSR was economically stronger than the whole Western nations of Europe? There is nothing today that would suggest such a thesis. Why do people believe in the pre war, "missing data", post war nonsense. In retrospect, Putin did not solve the problems that were present in the Soviet Union, hence there is nothing that could cause such considerable fluctuations.
Chinese values are simpy not honest. They also differ for urbanized areas like Beijing and the rural parts. China possessed the largest economy for the most time throughout history and we all know how useful this stats are for anything before the 18th century, observing such data in "historio-economic" literature can only be regarded as either comedy or a mean spirited joke.
There is a correlation between transparency and stat accuracy. Not to mention that life expectancy represents just another artificial value in itself (the funny thing is that one could argue that the cheap chinese labour and market increased the living standard of the average american, more goods more consumption).
I will give you some nice contingency examples which contradict the numbers: Iran vs Iraq. I would put all my money on Iran.
South Korea vs North Korea would depend on which side would be supported, my bet is on South Korea, Chinese (hidden) intervention could change it.
Another odd one with high, per capita values (fiscal paradises): Luxembourg. This is self explanatory.
Another one, hypothetical: USSR attacks a western country like Germany or France first (before 1941), my bet is on the defender (plenty of examples in history). You were also wrong about the K/D ratio of Soviets/Russians vs other nations, the exchange rate with the Wehrmacht was the highest yes, but the DLEDB Database shows that even a "poorer" country like Japan managed to inflict higher losses, while possessing less men (in the attack, 1904).
From this we can deduce 2 things: Tactical proficiency is falsely assessed or the GDP data is just worth a damn. The further we go back, the less reliable they are. The less transparent the data, the less accurate it is.
Here is what I believe: I think that all authoritarian states generally hide their military capabilities (or at least try to do it), opposed by all western democracies being rather undermilitarized. It is a matter of night and day, exploitation vs consumerism (this is also interesting as men become softer under certain conditions, higher living standard vs extreme conditions, they do have a higher amount of food though but something as Ghurkas are more natural soldier material). The values are a good prediction for transparent systems, not so much for the opposite, in the end its the question of how much you can and are willing to bleed. So what saves the Western World? Originally that was always their technological superiority.
You will end up with something like this: Germany, rich dictatorship, most powerful fighting power per capita. Soviet Union, largest military complex both dwarfed by the United States economic might.
Translate into modern times: IDF: Most experienced per capita, Russia: Largest firepower accumulation on land, US: Naval presence.
Highest theoretical potential: China, US, India, Brazil, Japan (yes they have a more powerful Army than during WW2).