First, some facts. The musket was NOT "the most powerful weapon." That would have been cannon, and several militias at the time DID in fact own and use cannons.
I thought of that, and almost included it, but it was so silly I left it out. Unfortunately, your interpretation of "militia" using the modern definition makes your entire argument wrong. The militia, as referred to in the Constitution, is the Army; the "people" are civilians. The purpose of the amendment is to maintain an armed civilian populace against an armed Government. Canons were powerful, but because they were less mobile, were not the most powerful weapon of the time. Either way, I'm not aware of any individuals today who own nuclear weapons.