Lenin was very serious about staying true to Marx, to the point of quoting entire pages to be sure he's not taking things out of context. His work is Marx's thought applied to economical and political developments Marx couldn't have foreseen, but it's in no way revisionist. I think this is why Stalin called it "Marxism-Leninism", to make sure it's clear this is Marxism.
Still you have "orthodox Marxists" who will claim ML is not really Marxism but I think if it was called just "Leninism" it would've been even easier for them to claim Leninism isn't even Marxism.