Maybe I am misunderstanding your question. It is ,of course, one of the problems is that of "vanguardism" but that term is not comprehensive enough...though I agree with you, one could argue that 'vanguardism', it could be argued, is the root of the other problems...lack of democracy, corruption, cynical power politics, dictatorship of Proleteriat, the State etc. So, maybe even if one could argue that it is the source of the problem, that it needs to be nuanced and broken up into its components.
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CB: Do you have a different source than Marx for the idea of the dictatorship of the proletariat ?
How would vanguardism be at the root of the problem of the State ?