Well the point of our (the US's) representative, multi-branch, democracy is to create multiple layers of oversight in our ruling process. Three branches of government balancing decentralized power with the electorate maintaining or overhauling said branches every so many years.
Compare that to what we used to have - hereditary monarchs with absolute power for a lifetime.
Far less oversight. Far fewer opportunities for course adjustment.
I think of the Federation as being a democracy to the nth degree. Power decentralized to the general public, and the system working somehow. The Federation Council is there to make that
work, and alternately to govern in ways that the public can't - say when decisions need to be made quickly, without time for larger debate and vote. Until there's some sort of Collective going, there's no way for the general public to vote on all things at all times, so you do need something left of the old republican system.