Yes.
Yes.
We ARE beyond dispute a representative democracy.
But there are things a simple majority cannot do in our system- a supermajority can, of course, do anything.
A simple majority cannot retain (or "grant" to use the disgusting common phrasing) new rights to the people, nor can a simple majority grant new powers to the government.
Both have to be done by a supermajority through amendment of the Constitution.
This requirement for a supermajority is neccessary for the Constitution to survive
.... and that is why we emphasize here the 'republican" nature of our government.