I think one thing that’s confusing is that there’s Marxism, communism, Leninism, MLM, etc. Different communist countries try to learn from other countries and each one has its own implementation based on its own material conditions.
From what I’ve heard, Lenin’s vanguard party and violent revolution thing was basically theorized to be required basically because of the long history of more peaceful movements being squashed by violent capitalists, the difficulty it is to wrest power from the old dictatorship, that of the rich, and the difficulty it is to change a country’s culture (see the super brainwashed US that might re-elect Trump let alone ever be able to get affordable health care). It’s not really required for communism so much as seen as a working theory of what’s required to achieve it in a pragmatic way due to the US trying to destroy it in every country that’s gone near it from its very inception and their full corporate-owned media blitz on people like Bernie or the democratic socialist in the UK.
A lot of the authoritarian nature of these countries is due to the material conditions from which they arose (usually poor, rural non-industrialized dictatorships, often colonized) and from which they had to stay alive (which is usually in a siege mentality as the US or other Western countries continued to sanction and undermine them). I’d definitely prefer to live in a Nordic country than any communist one, but they also started off in very different contexts, so I’m not sure if that will always be true. Like the other commenter, I’d be curious to see more data. I’d give the point to socialist countries right now though, because the experiment of capitalism has the entire global south counting against it.