Earlier quoted context omitted.
The US (with its support of the military) has been at war in the Middle East for nearly 2 decades now with insurgents. The argument is not that a rebellious citizenry will necessarily win a war, it's that it will draw out a bloody civil war so long and so expensive as to be a form of mutually assured destruction, the risk of which acts as a check in and of itself.
The fact is that the dictator would still win. The rebellious citizenry would live a life of absolute misery, just as those in the middle east do. The 2nd amendment made a lot of sense when weaponry consisted of horses and rifles, not computer-guided missiles. If there was ever a true US dictator, the 2nd amendment would mostly be used by the oppressed to rob, attack, and oppress one another.
The only effective bombing campaign that subdued a citizenry outright in military history were nukes, and if we ever crossed that line as a nation where the government nuked it's own citizens to quell rebellion, we are never coming back from that as a nation. It would leave a scar on humanity. Whatever would be left of the United States after that event would curse the people that did it.
So to your point, the 2A is not antiquated, if the US government had any interest in having an intact territory, at some point it would need to get face to face with the people, and the presence of firearms in the citizenry acts as a check against this possibility, and an escape option for the citizens of it ever got there.