How many of them are running roughshod over their (nominally) legally binding mission like the US government?

Probably all of them, to some degree or another, although not every culture considers the US libertarian ideal of limited government (much less the right to keep and bear arms) to be necessary, so any realistic answer to that question would probably be more complex than you're implying. But, where remedies within a political system exist, then the system can't be assumed to be tyrannical.

An equivalence drawn between the US and other governments would seem to suggest that civilian gun ownership doesn't deter the violence and corruption of the state, nor does its absence elsewhere appear to have led to the inevitable slaughter of those populations for whom gun control is much more strict than in the US.

Rather, it seems that when one enshrines into the culture the precept that the only free state is one cultivated by popular violence, it gives both the state and the people an excuse to justify violence as being an unavoidable cost of civilization. Political and social alternatives can't be seriously considered when, for many people, all other roads lead to slavery and death.

Instead, mass shootings in the US lead to a spike in gun sales, because they're effective advertising and recruitment tools for the NRA, even as the police and the government are becoming more militarized and surveillance more aggressive, in no small part because after 9/11 the American people wanted them to be. And if it's the case that the US is a more tyrannical state now, then I believe that's due to American democracy having worked as intended, rather than that tyranny having emerged from a vacuum, or some implicit tendency of states to creep towards totalitarianism.