I tend to interpret ‘tankie’ to be people who support Lenin’s dictatorship of the proletariat or similar ideas

That’s just Marxism. That idea started with Marx, not Lenin. He even talks about it in the Communist Manifesto, saying:

We have seen above, that the first step in the revolution by the working class is to raise the proletariat to the position of ruling class to win the battle of democracy. The proletariat will use its political supremacy to wrest, by degree, all capital from the bourgeoisie, to centralise all instruments of production in the hands of the State, i.e., of the proletariat organised as the ruling class; and to increase the total productive forces as rapidly as possible.

Not even mentioning his Critique of the Gotha Programme where he talks about the dictatorship of the proletariat and the transition from capitalism to communism extensively. It’s okay to not be a Marxist, but it’s just factually incorrect to claim that the dictatorship of the proletariat isn’t integral to Marx’s understanding of the transition to communism.