How do you explain the fact that the same Soviet (as much Russian as Ukrainian) army could not defeat tiny Finland in 1940 but was able to stand ground against German army one/two years later?
History is full of paradoxes and the failed Finnish campaign could be responsible for derailing Hitler's calculations.
Russia "was able to stand ground against German army one/two years later? "
Let's translate that from Russian.
"Russia was able to kill one German with 100 Ukrainians and Siberians at Stalingrad."
Stalin was smart - he put his nationalist enemies in the breech virtually with pointed sticks to stop the Nazis.