Regulated means regulated, and the current definition works just as well as the historic definition.
The gap is that you're assuming regulated means regulated by the Federal or state government. It does not, and in fact if you learn about the Bill of Rights, you'll find the intent was to guarantee the protection of rights the founders thought were natural civil rights. The core Constitution and Bill of Rights do not grant rights to the citizens; they recognize those rights as inherent and set limits to the powers of government.
The Federal Government intended to provide for the training and armament of the population. What happened was that after 70+ years of organized militias (the founding years through the Militia Acts), our governments realized the professional soldiers were far more effective in fighting wars, and cut funding to the militias. It's still advocated - see the Civilian Marksmanship Program - but neither mandatory nor comprehensive.
Gun rights activists like to point to Switzerland, and they are right except for one issue: in Switzerland, every conscripted citizen does get a fully-automatic assault rifle, but at the same time, that person is also trained in citizenship, ethics, military discipline, and handling of their weapon. But how do you think Switzerland would be in 150 years, if all other things stay the same, they were to continue providing assault rifles, but stopped educating?