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.
It's quite a feat to lessen your capabilities, and still be able to repel an invasion by all of Europe (sans England, as well as smaller countries like Switzerland, Ireland etc.)
The other view is Stalin had loyal cadre around him during the war, and did not have lieutenant colonels with links through the high command making bomb attempts against him.
It is quite clear that USSR's surprisingly weak performance in Winter War did encourage Hitler to think that he could crush Soviets with a quick summer war.
Most of Europe was being attacked (or actively suppressed) by Germany, not attacking the USSR with Germany, and even Germany was fighting on other fronts, so it wasn't even “all of Germany”.
Of course, these "national" liberation movements where double betrayed when the german racism became obvious.