I think its more about how power is distributed, regulated and mitigated within a political system that makes the difference - and the important factors here are independence of regulatory groups. For example, citizens rights without an independent judiciary are rendered politically impotent - What makes them valid is the capacity of the judiciary to rule against the state and the 'popular opinion'. If they can't then rights are meaningless.

Democratic systems tend to function inefficiently, but effectively, because they have degrees of distribution of power, systems of mitigation and regulation that are enforced by independent systems.

Yes. If the safe guards are removed then tyranny is always possible.

I think its inevitable, well not Tyranny in the true sense, but the general sense of a society that increasingly oppresses and suppresses the rights of at least some of their people - typically at least minority groups.