But I think a fairer comparison would be the US to the Empire, and not to the rebels.
I don’t think WWII is a good comparison - since the galaxy literally resented to a pre-ANH state, it’s simply US vs Vietnam all over again. But the impression I got from TFA and TLJ is that we have again the Empire with limitless resources and Vietnam, now instead of having a fleet, having a 50 year old ship.
But it hasn’t reverted to a pre ANH state. The First Order is just starting it’s campaign of conquest. They haven’t take over anything yet, except maybe the major hyperspace routes. Pre ANH, the Empire was at the height of its power. The Empire is Nazi Germany, even down to the helmets, stormtroopers, and how the Chancellor rose to power. Where we are at in the ST in terms of real world WWII, would be if the Nazis had risen again in Argentina and set out to conquer Europe all over again. They are at a severe disadvantage and it won’t be easy to do. They will meet with resistance in some corners. So it makes sense to compare it to the conquest of France. The First Order rose out on the Rim so they are far from their home systems and support.
I really don’t know why you guys are taking the First Order conquest of the galaxy as a done deal. There is plenty that says it isn’t. The word reigns really got you, didn’t it. I think it was hyperbole for effect. The rest of the crawl and the movie dialog all say it hasn’t happened yet, though it is in process. If it hasn’t happened it can still be stopped. And even if they take some of the easier systems, that leaves the harder ones that Leia and the resistance can coordinate into an effective opposition.