Long read, but even skimming through this may change your mind.They, the USSR, had no shortage of scientist able to help them advance in rocket science. What evidence is there that they did not also capture Germans who had worked on atomic bomb science? I disagree about the Soviet's limitations. I think they would have reached production and testing before and without an altercation with America.
If they had Atomic scientists, they would not have risked using spies like the Rosenbergs. They needed a platform to build on. They needed the ideas of Oppenheimer and Einstein to get them off the ground.
cns.miis.edu/npr/pdfs/72pavel.pdf