Even the wiki on the Rosenbergs backs up the idea that the spying likely didn't accelerate development that much of at all

Lavrentiy Beria, the head official of the Soviet nuclear project, used foreign intelligence only as a third-party check rather than giving it directly to the design teams, who he did not clear to know about the espionage efforts, and the development was indigenous. Considering that the pace of the Soviet program was set primarily by the amount of uranium that it could procure, it is difficult for scholars to judge accurately how much time was saved, if any.

Like basically everywhere else, the major limiting factor was access to uranium. Not technical knowledge.