as PhD historian Jonathon House notes, the Nazis were extremely unprepared for a war with the Soviet Union: https://www.youtube.com/watch?v=zinPbUZUHDE
as amateur historian TIK notes, the USSR did not beat the Nazis with manpower alone: https://www.youtube.com/watch?v=_7BE8CsM9ds
despite having a smaller economy and facing millions of casualties, the USSR outproduced and outfought the Nazis: <https://warwick.ac.uk/fac/soc/economics/staff/mharrison/public/totalwar2005.pdf> Yet table 1 showed that the Soviet Union was not superior to Germany in overall resources. Although Soviet GDP exceeded Germany’s in 1940, German wartime mobilization and the deep invasion of Soviet territory shifted the balance strongly in Germany’s favour. In the most critical years of the war overall Soviet resources were only 70 per cent of Germany’s, and the increment arising from Allied aid compensated only to a small extent. It is true that Germany was engaged on two fronts. Taking this into account, the Soviet Union still maintained a bigger army in the field than Germany and outproduced German industry systematically in weapons other than warships
