No, democratic centralism effectifly prevents this, by having elections from bottom up and- this is important- by having every legislative body be accountable to the lower one, meaning that people who would be power greedy and this resulting in breaking promises or bad handling of issues in power, were stripped of their ranks when the bottom legislative body reported them to the responsible comitee. This combined with a regular report on the work of each body/high positioned leader and a critical and self critical evaluation of the work oneself has done, safeguarded the vanguard from those power hungry careerists.
The downfall of these socialsits state where not the fault of a few "bad apples" that where "overseen" by "good" Communists and destroyed the Socialist states, this is an inherently idealist analyis of the demise of socialist states
If we analyse the counterrevolution of 89' through a materialist lense, meaning that we look at the economic and cultural changes that led people develop a specific trail of thought and act in a counterrevolutionairy way, we see that primarly there where mistakes that the communist parties did that led to revisionist ideas grow inside the party and creat apathy from the masses to the party.
Namely this would be communist partíes losing connections to the people,the same old people inside the party congresses, not much change in the country, a state apparteus that wasn't a dynamic between state and people rather an apparetus that just guarded the status quo and didn'T change much else.
This combined with an influence in western idealism inside the GDR for example gave fire for people that were tired of the current political crusted system and wanted *new* things, fancy western fruits, coca-cola etc.
Revisionist tendecies also grew inside the SED with people like Gregor Gysi and others advocating for "democratic socialism" losing connection with Marxism-Leninism, even many SED politicians filled the streets and protested for an end of the "SED Dictatorship"
In the Soviet union I would probably say that stalins neglegtic of keeping the Socialist democracy vivid with increasingly infrequent meetings of the Central Committee and Politburo and a long delay from the 18th Congress in 1939 to the 19th in 1952.
This lead to revisionist like khrushchev coming to power and his unmarxist evaluation of stalins mistakes gave further growth to revisionist tendencies, Breshnev, while not revisionist in policies or else, kept things at a status quo, not keeping party life vivid and not working on the socialist state, helped revisionist grow further. This ended in Gorbachev who threw all of Marxist-Leninist thought and theory in the trashbin and proposed social democracy and killed the soviet union
In conclusion we see that democratic centralism wasn't at fault for the demise of socialist states, rather its usefulness wasn't exerciced enough and this enabled traitors to rise to power.
Democratic centralism by itself is the most effective tactical tool Marxist-Leninist have. It enbodies freedom of discussion and unity of action, it combines the power of Marxist-Leninist thought and puts it into praxis, with a vanguard party at its top. Without it communist parties wouldn't be more than movements, mere loose connections of communists, without a competent leadership, without unity of action, resulting in a uncoherent praxis without direction. No Socialist state has ever been achived without a vanguard party and democratic centralism
