While I think that is also a very interesting topic and I'm sure we would agree on many things, I'm not sure it helps to get into the philosophical argument while talking about real-life political systems and the different flavours of representative democracies.
I don't think i am, sorry if it sounds like bikeshedding. I'm interested in the practical question of who holds political power, and who holds the "legitimate violence" to enforce this political power.
If me and my neighbors can't "legally" define our own sets of rules and regulations (which we can't in France), i just can't call that a democracy. Time and time again i've witnessed local communes get crushed by national/industrial interests... that's a very practical concern, not philosophical, whether you can keep your home and your life or they're going to destroy your entire village like they did around the Hambach charcoal mine (or like they tried in NDDL, or are still trying in Bure).
If you and your neighbours want to not be subject to the French government, you can always go somewhere else. The fact there’s probably nowhere better for you to go is hardly France’s problem.
Of course some systems implement forms of direct democracies, although they are not represented in the UN because they are not taking part in the "game of thrones" of international politics. But saying that no Nation State implements direct democracy is right on point, because "democracy" is the very opposite (by definition, i.e. "power to the people") to the State ("power over the people").
In contrast, most States on Earth (even Kingdoms!) implement forms of representation/election. Now, can we even call that a democracy? Electoral systems as we know them today were designed in the 18th century by french and american politicians/philosophers who were strongly opposed to (and afraid of) democracy so that's a bit of a stretch.
I mean take a very simple issue: ask everyone "should some people be sleeping on the streets when there's millions of empty dwellings?" and they'll all say "no". Now see what the government is doing with this popular will, and you'll understand government don't care about the people and wipe their asses with our needs. Call me "cynical" if you will but i'm certain the people who uphold Nation State have no expertise, and certainly have material interests opposed to ours.