You haven't told us your reasons for doubting it, so that's hard to answer. But neither "communism" or "democracy" is a sufficiently well-defined concept to be of any use for the important question you want to raise. First, it's essential to distinguish between the historical governments that described themselves (or were described by others) as "communist" (or whatever) and what "communism" might have meant before or after that as an aspiration or a political or social ideal, or even just as a description. These are entirely different things and often have no relation to each other at all. Second, there is the question about which features of a given society "matter" in the sense that they actually characterize how the society "works," i.e. that they influence other parameters in a society and determine what happens in it, how people are treated, how rich they are, etc. Insofar as we know anything about this at all, such outcomes generally have little to do with the extremely crude terms generally used to describe political and economic systems: liberal democracy, fascism, capitalism, authoritarianism, dictatorship, oligarchy, and so on.
You would think, since this subject is of such extreme importance for human welfare, and of such intense concern e.g. to all the many people who have strong political opinions, that there would be an academic subject, or a discipline out there somewhere, in which a more rigorous and empirically defensible classification system or taxonomy of institutional configurations could be found, and in which the outcomes of the various configurations so defined were compared in terms of, say, individual autonomy, wealth, life expectancy, adaptability to change or migration, quality of life, social conflict, and so on. But no, there is no such thing! The closest thing we have are the very tentative gropings in development economics, in the theory of economic growth, and in the corresponding parts of economic history, to study the institutional contexts of growth and development, the distributional and welfare consequences of those institutional frameworks, and such things. On the surface the conceptual sophistication of these studies can appear to be quite advanced; economists who engage with these questions employ evolutionary game theory and other dynamic modelling resources, but actually the models, so far at least, have little or no empirical traction. In fact, our empirical knowledge of institutional systems is appallingly thin; as I said, we don’t even have a way of characterizing different systems, though we do know that some past and present societies worked very differently from each other in specifiable ways. But very few people are even working on this stuff, and the effective conceptual sophistication of the study of institutions hasn’t really advanced beyond the third book of Hume’s Treatise (I do agree with Russell Hardin that Hume was way ahead of his time, but that doesn't excuse our abject ignorance two or three centuries later).
You might well think this a scandal, and you would be right. Why aren’t people working on these questions that are of such urgent and obvious importance to human life? Why aren’t these questions at the very center of academic discussion? Well, partly it’s a typically academic pathology: economists are rewarded for doing theory, not empirical work, and historians are not interested in economic or institutional history any more. Economic history, until a decade or two ago, was a central and respectable part of the academic discipline of history, but that has largely died out; economic history is now done almost entirely by economists. And economists simply can’t afford the detailed and painstaking (and partly qualitative) empirical work that is required to figure out how a local or regional society actually works, because that kind of work doesn’t get you even into the economic history journals these days (which are now all run by economists), let alone the mainstream economics journals you need to publish in to get a job in a good department. So in the near term, at least, there is little hope that the situation will improve.