That being said, there probably aren't any capitalist societies today; capitalism was the dominant system of the advanced societies if the 19th century, so banned by various Socialist (including Communist, Marx in particular) critics of that system. Most advanced economies today are mixed economies which retain some features of Communism as well as substantial departures afford specifically to address the problems identified by critics of the system. While it is neither, the modern mixed economy resembles a form of socialism a much as it resembles capitalism. Actual advocates of capitalism, of which there are many on the right, seek significant changes to undo the departures from capitalism introduce offer the last century and a half or so.
We've tried capitalism and Leninism and various variations on the modern mixed economy, of those Leninism and the modern mixed economy each have some (but not the same subset) of the features that differentiate Marxism from capitalism. You could as well say we've tried Marxism and it proved better than capitalism (based on the modern mixed economy as a form of Marxism) as you could say that Marxism was tried and failed (based on Leninism as a form of Marxism.) But really, capitalism fell, evolving in a direction similar to -- but still distinctly different from -- that suggested by Marx.
A long series of failures only proves that those specific things didn't work. You need more than that to come to a final conclusion.
