Leninism is not a replacement of Marxism, Leninism refers to Lenin's own advancements on Marxism. Lenin used Marxist analysis to bring Marxism to a new era, from the era of industrial capitalism to the imperialist stage of capitalism. The primary advancements of Leninism are the following:
- The Leninist strategy and tactics of revolution
- The Leninist critique of Imperialism
- The Leninist understanding of the national question, and the right of self-determination.
Marxism-Leninism is called as such because the basis of Marxism-Leninism is Marxism. Marxism-Leninism carries over the 3 basic fundamentals of Marxism:
- Dialectical and historical materialism as the guiding worldview
- The Marxist critique of capitalism based on the Law of Value
- The scientific approach to socialism, grounded in class struggle.
In the modern era, the number of Marxists that reject Lenin are incredibly fringe. Lenin's work as a Marxist is incredibly obvious to anyone who has read both Marx and Lenin, and it's very clear that Lenin was history's greatest Marxist, after the deaths of Marx and Engels. MLs are the dominant form of Marxism in the modern era, and most relevant historically, so trying to claim Marxism-Leninism isn't Marxist requires an enormous level of justification on your part.