The point about cannons and warships actually makes it very clear about what the authors' intent was re: balance of risk; at the time, private ownership of artillery was completely legal and unregulated. Private citizens owned warships with dozens of live cannons that could bombard coastal cities, and didn't even need to file paperwork to do so! A warship can cause quite a bit more mayhem than a glock.
Legal yes, protected by the constitution without constraint no.
Both the use of Arms being man portable weapons and militia makes a very clear distinction.