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.