I suspect one of the reasons Stalin’s defense of the Ukraine at the beginning of Barbarossa was next to non-existant, is because that was where the majority of the Soviet Union’s Jews lived. Hitler could take care of his “Jewish Problem” in the meantime, before eventually Soviet defense stiffened and ultimately turned the tide of the war.
Probably also due to the fact that he purged the military in 1937, sending some of the best officers to rot in gulag, and demoralizing the rest, and the fact that he honestly thought Hitler was his best bud and would never ever attack him, so he didn’t plan.
I once knew a man who lived in a small Polish village in the Russian-occupied side. The Soviet officer allowed German officers to walk through their positions freely. They took notes, made plans, and then attacked all the weak points and just rolled the Soviets up. My elderly friend escaped on horseback and fought in the woods as a partisan. He was 13 at the time.
The Soviets fought quite hard in Ukraine. They lost entire army groups. Well over 1 million dead.