The BV’s were initially grass roots, along with other communists in Russia at the time, but after Lenin got control the policies all came from above with little to no input from the workers below, and the BV’s became the defacto only party.
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:
