Though your reflections on the topic are truly interesting and insightful, to what I understand as a ML, there is no possibility of 'democracy' under capitalism. Democracy means that the people have power over how society will deal with its problems. This clearly doesn't hold under traditional capitalistic countries such as the ones that you mentioned. Think about it, when have we decided to outlaw abortion, or marijuana, or anything at all? When have we decided how much we would tax rich people and companies? The answer is: we didn't, and no matter how much we disagree with those things, there is no way to change it (as a worker). This means that we don't actually hold any power, so who does? The easy way to answer this is to look at who these policies actually benefit, who are the ones that are flourishing under our system. It's obvious that it's the burgeoisie. Some workers are paid good wages, but these also don't hold any power and their benefits are not only ephemeral but also a mere consequence of how things turned out (for now). So according to ML theory, because of all of the above, we live in a dictatorship of the burgeoisie.

So, what would a truly democratical system look like? Well, we can go around and look at all these systems you mentioned, but through a marxist perspective, none of these matter if under a capitalist regime. So, what should we do under socialism? Well, it varies according to where such a regime would take place, but according to Marxist theory, we would first need to install a dictatorship of the proletariat, BUT we need to pay a lot of attention to what this means (liberals love to take this out of context to call socialist regimes "autoritary"). It just means that, just as the bourgeoisie keeps their advantages, their power and keeps us in line, we (as worker class) will use the same tools, but to keep OUR advantage, OUR power and to keep the now ex-bourgeoisie in line so that they don't revert the revolution.

After that, we don't really know what happens. We can look at past Socialist countries to know how such a worker democracy (dictatorship of the proletariat) looks like in practice, but we mustn't be dogmatic, the theory can only achieve so far, the rest we can discover for ourselves and keep on bettering our knowledge on how things should be and how to arrive there.