Uh, go back and re-read the Constitution. The amendment process requires the accession of both Congress AND three-quarters of the state legislatures--that hardly makes them "irrelevant". And in fact, the state legislatures have the specific power to bypass the Congress completely, by issuing a call for a new Constitutional Convention. Power never before used, but definitely available to those "irrelevant" state leigslatures.
And yes, amending the Constituion "does" make the point of the specific judicial review moot---but it DOES fix the problem in a Constitutionally correct fashion. NOT by have the Supreme Court judges legislate from the bench, as is currently the case.
They did use that power once -- in 1787. They called for a Constitutional Convention to amend the Articles of Confederation to fix the tax problem. But those gathered for the Convention started out not by amending the Articles of Confederation, but by throwing the whole thing out and starting from scratch. In all probability the same thing would happen with a new convention and we would end up with a 150-page beast like the European Union Constitution guaranteeing everyone a new pony, making "Kumbaya" the National Anthem, and declaring smoking a capital crime.