It depends entirely on how ruthless the standing army of 500,000 operates. If it operates as the Soviets operated after they had won their Civil War, in their suppression of Ukraine for example, it would be done rapidly by deploying modern logistics and modern weapons while interdicting logistics, as described.
If, on the other hand, the standing army of only one half million attempted to occupy a continent of 300 million people the way we occupied Iraq, I agree, it would be an undertaking bedeviled by the same factors that frustrated the redcoats and 1775-1781 and the Americans in Vietnam.
I do not believe the situation in America is similar to the Nazi occupation of the vast reaches of the Soviet Union in 1941 and 1942 where armed resistance was a very real factor. Modern America lives on the grid, lives on the Internet, lives on supplied water, lives on petroleum, lives on food deliveries all of which could be quickly interdicted. That remedy was not available to the occupying Wehrmacht against an essentially agrarian economy.
Under these circumstances putting down an insurrection is not synonymous with occupation as we saw in Iraq but more like occupation that we saw in Japan.
The moral of this analysis: rebel only against a government of the right which is tethered to the Constitution and to morality. If this analysis describes the reality, it seems that the Second Amendment is valuable only to deter a leftist government, unmoored from either, from outrages against the people but not a means of victory in open warfare and effective but probably unnecessary against a conservative government both for deterrence and resistance.
