Actually another good reply to that common myth would forego the whole "apply it to the other amendments" idea. And simply refute the actual statement itself.
The founders were not idiots. Weapons and their lethality has been steadily advancing and improving throughout history ever since weapons were invented. From sharpened rocks, to spears, swords, bows and the flintlock muskets that they were so familiar with.
It would be ludicrous for anyone to think that we would have just stopped at muzzle-loading flintlocks and called it good enough.
While the founders may not have envisioned M16s and AK-47s specifically they were well aware of the fact that weapons would become faster firing, more accurate, and longer ranged.