There are no Madisons or Washingtons or Franklins anymore. You're correct that the people who wind up at the convention will be politicians. The same kind of people that got us into this mess to begin with.
No restoration of republican freedom is possible without its repeal. Not because the states are wise, but precisely because they will look out for their interests, as per the Framers’ design.
Our backs are against the wall. Even if the dangers are as you say, our once republic is now an authoritarian state, where the law is what Obama and his criminals say it is.
We have nothing to lose.