No part of Leninism, in theory or practice, supports the idea of a single, near-totalitarian dictator. The term "dictatorship of the proletariat" originates in the era of Marx, and refers not to any individual dictator, but the working class itself as the rulers, makers, and dictators of society. The heads of state in socialist countries have all been selected with democratic processes, be they approval votes, votes based on elected delegates, etc. The heads of state have not had absolute power either, but instead often have less power than, say, the US head of state.
The necessity of a single party is because socialism is, in effect, a unitary system meant to represent a single class, the working class. Democratic centralism does not mean the absence of democracy, but the absence of organized factionalism and opposition within the socialist system. The necessity of a single system was already present with Marx, the advance of the vanguard path to socialism by Lenin was made based on Marxist understandings of class and the state.
If you believe Lenin is bad, then thinking Marx was good is hypocritical. Your issues with Lenin are based on a combination of sanitizing the views of Marx and accepting bourgeois misdirection about existing socialism as fact. If you truly believe Lenin was bad, then Marxism itself should also be seen as bad.