The Constitution does not "grant" the power to keep and bear arms. It, instead, prohibits the government from infringing a pre-existing right.
The author misses the point that governments derive their just powers from the consent of the governed. The governed at the time did not consent to allowing any limitations on the right to keep and bear arms.
The amendment process was included to allow their successors to consent to granting the government additional powers. The author is correct that this is the way to go.
If the sorryassed electorate wants to give consent to "arms confiscation" - then we have just taken a turn down that road to hell have we not?