I tested this in HOI4 with Japanese help and it didn't make much of a difference, I still lost as Germany. Japanese simply couldn't get through the Soviet-Mongolian line and my offensive stalled out.
You heard it here boys, proven by conclusive scientific data.
:/ ive beaten the soviets multiple times in 1941 without japanese or italian or romanian or any axis powers help on the eastern front on the hardest difficulty that isn't conclusive scientific data LOL
hitler could've done a lot of things, labeling the assault as the "liberation of ukraine" would've certainly brought many to the german side usage of captured manpower such as putting them into Andrey Vlasov's liberation army would have also helped
hitler wasn't aware from his generals the army had to resupply every 800km~, he just kept pushing forward
not securing moscow and instead encircling Kiev was also a big mistake, taking moscow would've hurt morale severely
emphasis on pushing southeast to the Baku oil fields would have helped resourceswise
hitler didn't use the immense mustard gas armory the germans had at the time either
hitler didnt listen to his generals and instead believed he could command and set up lines by himself (failure)
many things, russia could've fell their numbers were large but would eventually become obsolete if morale fell