Marxism-Leninism was synthesized by Stalin, but Stalin himself did not add much of anything to Marx, Engels, or Lenin, aside form sharpening Lenin's analysis of the national question, which is particularly important for indigenous struggles (and also partially why a group of indigenous American tribes named Stalin an honorary chief in 1942, presenting him with a headdress).
Marxism-Leninism is not "pro-dictatorship." This is a simplistic framing of unitary forms of democracy that focus on policy changes as the primary issue of political engagement, rather than party changes. States like Cuba, that are guided by Marxism-Leninism, have complex systems of delegate-based democracy.