First would dispute some of your logic. The second amendment of you constitution says: "A well regulated Militia, being necessary to the security of a free State...". So to me the clear intent was to make sure that the early US government had a body of armed and trained civilians to call on to defend it should Britian, or any other European power, decide to invade. This goal did indeed make a lot of sense 200+ years ago but not so much today. However importantly the clear aim was the defence of your country i.e. not to fight against your government but to fight for it against foreign invaders. If you want to have a look at a "well regulated militia" today try Switzerland. They arm, but also train their citizens. The result is a well regulated and trained militia but very few deaths due to gun violence.
Secondly though there seems little point for the law in today's world. The US has a huge military force and it is just about inconceivable that it would ever need to rely on armed citizens to defend itself. That same force means that even you interpretation, that citizens need guns to hold the government to account, is also irrelevant today. There is no way that they could possibly defeat the US armed forces if they continued to follow the government's orders. The best defence of democracy today is the same as it has always been: the will of the people. Governments are made up of people and if enough people refuse to serve it, and many resist it, it will fall.
So I agree that there was a very good reason for the law initially. However now the actual aim of that law is being completely ignored and, in today's world, the aim is irrelevant anyway. If you cannot change your laws to deal with changing circumstances you will end up in a lot of trouble.