That stands in direct contrast to the actual structure of the USSR, and a misunderstanding of Democratic Centralism. The Soviets were the organizational organ of the USSR, as shown here:
Secondly, being a single party does not mean democratization lowers. Parlimentarianism obscures the material impact of a Worker’s voice. A single party system can be bad, such as in Nazi Germany, where there was little to no actual democracy. A single party system can be good, such as in the USSR.
As per your previous statement that “most of us want bottom-up revolutions,” that’s correct, but “most of us” do not agree that the October Revolution was a “top-down” revolution.
I recommend reading the following texts, if you have not done so already: