Your and your opponents' problem is that you imagine the figth happening the same way as classic (symmetric) wars, out on a battlefield or each sides with their own separate territory with a frontline inbetween. But that's not what is happening in such cases, or at least when the rebels know what's good for them.
The way to fight such a war from the rebels' side is to not square up directly with the government's forces. You don't go out onto battlefields, or even just separate geographical areas. You are staying/hiding/living among and intermixed wiht the general population that the government rules over.
They can't nuke/bomb/shell you because that would cause the government itself damage through:
- large number of non-rebel casualties, primarily resulting in more people becoming rebels or even a more wide scale uprising among the general population on wich the state relies to support itself and if the scale of destruction is large eough, then the loss of a critical proportion/all of the population resulting in immediate collapse
-damage to non-human assets, think infrastructure, valuable resources, etc.
-direct damage to the members of the government themselves (them becoming collateral damage). remember: the rebels are around them, mixed in the general surrounding population.
Example: the u.s. turned into an totalitarian, opressive state. there's a rebel movement. the government found out, that there is a relatively concentrated mass off rebels in a neighborhood of inner city new york. do you think that they could just go bomb/nuke/shell it?
The way they would have to deal with such an insurgency type war is to get boots on the ground and go up close and personal. and that's where firearms owned by the rebels come in: it allows them to repel the immediate attack, escape, and spread out into and hide among the general population again. These "up close and personal" fights happen with firearms. Airforce, navy, artillery and such won't help you. In an urban environment not even small, relatively precise drones are good enough.
And the same conditions and environment of being mixed in with the general population not only makes regular firearms a viable, effective self defence measure, but also and effective weapon of offence, allowing assasinations of key paople, sabotage of key infrastructure and equipment and in general, a more equal field in destroying enemy government forces.
And that's just when we are talking about a very small number of rebels.
The larger the portion of the general population that opposes the government, the bigger the fight they can put up. And after a certain point, they can just overhelm the governmental forces with sheer numbers.
Imagine that you are the dictator. You have a loyal army with nukes, bombers, aircraft carriers. If the populatio is unarmed, you can send in your soldiers and force the people to obey. Now, if said population is armed, even if only with firearms, your soldiers can't just go in and make them obey, because the people can shoot your soldiers. And yes, technically you could then just annihilate your population with nukes, bombs, etc., but in reality you can't. You need the population for your existence. You can't have a dictatorship without people to opress and exploit. After all, these people are the ones who make your food, electricity, build and keep up the infrastrcture, and generate the wealth you do this entire dictatorship-stuff for. You need them for your existence. Your army needs them for their existence. Without the population, you don't exist. And while you can't destroy them, they sure as hell can destroy you. There will be thousands of them for every soldier you have, maybe tens of thousands.
That's why the right and ability to own firearms for the general population is an effective defence against the emergence of a tyrannical government.