A large fraction of the harm from firearms comes from their ability to fire rapidly which didn’t exist when the constitution was written. As such it was making a very different balance of risk between the general public and individuals.
2. As someone else pointed out, early repeating rifles did exist then.
3. If the meaning of the constitution is only to be evaluated against the technology available at the time -- what does that say about the validity of the 1st or 4th amendments with modern technology?
But again, in historical context, the point of the 2A was to permit people to own the most deadly weapons of war that existed at that time.