the germans split their forces too thin in Russia i believe. I mean northern army goes to leningrad (and starves it instead of sieging) one army to moscow one army stuck in stalingrad and one in the caucasus.
This and the bad weather and circumstances prevented the blitzkrieg to continue. They should have focussed on Moscow and then rush to the caucasus.
Forget the V2 and just build planes. Don’t bomb London with little fighter cover losing too much planes. They should have copied the RAF defense when defending against the air raids which costed them so much industrial damage.
Production was one of the downfalls of germany too. Too little fuel and resources on any given time.