Stalin expected a fast population growth, and when the 1937 census showed that he was mistaken, and population of USSR was only 162 million, Stalin had statisticians sent to the GULAG and some were even executed. After that, many tried to avoid being nominated for top jobs, out of fear for meeting the same fate.
https://en.wikipedia.org/wiki/Soviet_Census_(1937)
This kind of dictatorship and purges of competent people certainly lessened the capabilities of Soviet Union, lead to the unexpected result of the Winter War, and greatly increased the losses of USSR in the coming great war.