If NEP is what you mean by "decentralization" (because nothing else makes sense even remotely, Soviets by definition are a vertical structure, like a tree with its root being the center), then it's generally accepted that NEP was the thing which allowed to restore Soviet Russia from a famished wasteland after the Civil War.

so they centralized early

They had almost a decade of slowly pushing out communist dissenters out of the political field (all non-communist leftists were already banned closer to the end of the Civil War, and the rest - hahaha), which may give you the wrong impression. However, they were heavily centralized from day one. That was part of the ideology. It's not some European leftists we are talking about.

For these people political competitiveness or pluralism or due process in courts or human rights were not high on the list of priorities. Building industries to arm heavily and "spread the revolution" was.

Their ideal was some sort of a communist version of the German Empire.