In the past 400 years or so, it seem as though world power had been dominated by relatively small western countries that used colonies to provide them with raw materials necessary for goods and eventually industrialization.
Looking at WWII, the U.S. appeared to be in a position of tremendous advantage: instead of relying on distant colonies, their natural borders were gigantic compared to most other powers. It seems like this gave the Americans a huge boost to potential locations for major industrial hubs and increased access to diverse natural resources. It looks like there was no way the Germans or the Japanese could even hope to stand a chance against the Americans unless they underwent some serious infrastructural upgrades to their conquered territories.
Is the amount of land controlled a historically accurate way to compare the relative power of states? A related question: were the Germans and the Japanese on a trajectory during WWII to actually make use of and rival American industrial infrastructure and access to resources if they had not provoked the U.S.?
Are you speaking about purely military power? If so, then access to resources (within one's borders or via trade that is unlikely to be interrupted during wartime) is a more likely indicator than pure land area. Joseph Maiolo covers this a bit in Cry Havoc, with the various countries involved in WWII and their quests for autarky. However, if you are looking at other kinds of power as a function of land area then the tiny Vatican City (at a mere 110 acres) punches well above its weight class. Its military is smaller than the police force of New York City by orders of magnitude, but the Vatican's ability to shape events outside of its borders is significant.
Getting back to the military aspect of your question:
were the Germans and the Japanese on a trajectory during WWII to actually make use of and rival American industrial infrastructure and access to resources if they had not provoked the U.S.?
US production during WWII was simply staggering. The industrial potential of the United States allowed it to mass produce just about every item needed to make war, from bullets to battleships. Martin Van Creveld has some interesting things to say about wartime aircraft production. Beyond the pure numbers, he examines production as a function of industrial potential.
Taking the period 1940-45 as the best available compromise, we find that, in those six years, the United States produced 309,761 aircraft. Germany built 109,586, the British Empire 143,234, the Soviet Union 147,836, and Japan 74,646. Earlier in this chapter it was estimated that, if America's industrial potential in 1939 stood at 3, then the figures for Germany, the British Empire, the Soviet Union, and Japan were 1.2, 1, 0.8, and 0.5 respectively. Combining the two sets we find that Germany produced somewhat less than its fair share of aircraft. The British Empire produced considerably more, and the USSR many more. Japan, too, produced more than its share. This calculation ignores many factors, including the extent to which the various countries mobilized their resources and the types of aircraft each produced. Still we conclude that, relative to their overall industrial potential, all the main belligerents except Germany built more aircraft than the United States did. (emphasis in original)
So he cites German industrial potential in 1939 as a 1.2, Japan at a 0.5, and the US at a 3, and even though the US underproduced by this metric they still made 309,761 aircraft to Germany's 109,586 and Japan's 74,646. This method of counting also would make a Fieseler Storch count the same as a Superfortress when the latter was hugely more expensive. Bluntly, Germany was out of its league in terms of relative production to the US, and Japan was even further dwarfed. Van Creveld covers aircraft production, but for prewar industrial potential I would recommend Joseph Maiolo's Cry Havoc as it covers the arms race of the 1930's in accessible detail.