I think your post, while well thought out, misses the point of an armed citizenry. No one is realistically thinking a lightly-armed, poorly-trained citizenry can effectively wage war against a well-equipped, well-trained professional military force. Nor do I think anyone is suggesting a straight up guerrilla-style campaign for asymmetric warfare.
No, the point of an armed citizenry is to give the government pause. An unarmed populace can be brought to heel without much in the way of bloodshed. But an armed populace? Even a lightly-armed one means the government can't just march in and round up potential dissidents. There is the strong possibility of a firefight. Sure, the little guys will probably lose. But it means the government must escalate to lethal force just to get started on whatever nefarious course it may be planning for its citizens.
In a way, it's little like conventional vs. nuclear combat between nation-states. When both sides were purely conventional, wars were fairly common (call this analogous to both sides being armed with swords). When one side has nukes and the other does not, the side with nukes gets its way pretty much whenever it wants without ever having to drop a nuke (analogous to a police state with a disarmed citizenry). But when both sides are equally armed with dangerous weapons that require either side to really think about whether they want to invite a deeply damaging and dangerous conflict...you get very few actual wars (analogous to an armed state and armed citizenry).
If I'm unarmed and the government (for whatever reason) decides I need to be removed, not only can I not stop them, but I probably can't even inflict significant harm on them. They will most likely even take me alive, without a protracted fight. The risk to them in this case, both in blood and bad PR, is minimal.
If I'm armed and the government (for whatever reason) decides I need to be removed, they will most likely succeed. I will, however, most likely succeed in causing casualties and/or making a big PR spectacle of being taken down. I might even achieve martyr status if I'm killed, causing a PR debacle for the government. The government will want to avoid these things, thus they will try to find means other than brute force of arms to remove me. Or they might not remove me at all, deeming the political risk too high. This is why we need to be armed. Not as a credible army-in-waiting, but as a deterrent.