I think we've run afoul of two issues. How do you define Marxism-Leninism? Through which means do you know its correctness?
If you know its correctness through implementation and then measuring the results then that's science testing a hypothesis. For example I know my nose is between my eyes because I can measure through my senses and test that idea repeatedly until I have statistical confidence that's the location of my nose. If for some reason the location of my nose changes then that information can be updated with testing and measurement most likely through my senses.
If you know through some other means like spiritual revelation then it's still the case that the concept will have measurable outcomes we can use to test and compare with other concepts to verify its correctness.