You could also look at it from the opposite perspective: the military is now too powerful for private ownership of guns to do much and the downsides of having gun ownership now outweigh the nonexistent benefits
I.e. it's obviously reasonable to believe that private firearms cannot stand up to the federal government, regardless of whether it is the case under theoretical conditions.
Tell that to the Taliban or the Vietnamese. They took on a massively more powerful military, were significantly outgunned, and came out of it in control of their respective countries. If there's anything we can learn from history it's that war is incredibly chaotic and unpredictable, and that anyone making bold and confident predictions is just about guaranteed to have reality prove them wrong.
It shows a lack of understanding about the nature and power of insurgencies and a vast overestimation of the military's ability to protect itself should every military base, forward refueling point, and backyard airstrip suddenly become under attack. Hint: They're not really designed for that.