You need to fix you sense of scale first, the US didn't invade the whole of Africa, just the northern tip, it didn't do it alone and there was no native resistance, but foreign Italian/German troops, the simple geography of France is nothing compared to SA and the more difficult geography of Italy seriously complicated matters for the Allies. All that landmass more or less the same size an average SA country but we have much much more complicated geographical features.
So yes, square footage matters, terrain matters, population centers spread out in the countryside matter, and that's not counting the local resistance, what can tanks do in the amazon or the Andes mountains? where's your blitzkrieg there? even plains have a hard time in those regions, mix Vietnam jungles with ( far taller) Afghanistan-like mountains, then triple their landmass and you have your average Pacific facing SA country.
For example, the US actually drew up a plan to invade northern Brazil (to "protect" it from the Germans) and it found that it was way to difficult and expensive to do it not even counting local resistance, just taking into account the difficulties of landing troops in the jagged beaches of northern Brazil, the supply lines were a nightmare, etc. In turn they turned to diplomacy and after a while Brazil joined the Allies.
One would think history has taught several lessons about underestimating geography and strategic depth.
My point is that by making Minors more Fun, you make Majors more Fun, because they would all function under the same rules, and crazy stuff like conquering whole continents with a couple destroyers, transports and marine divisions shouldn't be possible. Which adds to the fact that industrialization and specially the mechanization of armies was so important in WW2, as a Major you really have to plan your countries military growth, your armies, your supply lines and supply depots, tackle those difficulties so you (as Germany for example) can have a beautifully executed invasion of Poland, France and then Russia, if you want more then you have to actually rely on minors in other hemispheres for bases, supplies, resources, etc.
I think, with the more realistic representation of geography and scale of the world in this particular game, it will be more fun for everyone, we can actually experience why blitzkrieg strategies work on certain terrain and on certain situations, and come up with new strategies and army compositions for other situations (something that Hitler failed to do in Russia for instance)
