The basic concept behind the infantry should be:Wehrmacht = few high specialised elite soldiersvsSoviet = many low skilled footmen + a little amount of good soldiers
The infantry of soviet union is not overpowered, but its obvious that a strelky section can beat volks and even grens if they do not use nades, because its a 6-man squad (or more)! You should use MG42 to suppress soviet infantry every time you can, or they will flank your infantry more easily.
There was in both army elite high-skilled troops and less skilled one
Yes, but the percentage of skilled troops in quality and quantity in the german wehrmacht was by far higher than in the red army. There were also other reasons for the strenght of german ground forces. The basic training was way better and more complex, the equipment was better and the commando structure was more efficient which increased maneuverability of german infantry. There are a lot of books about this ("Fighting Power" by van Creveld is one of the most scientific), but a simple look on the ratio of casualities of battles during the russian campaign gives an answer to this question.
If you fight against AI soviet thats normal. AI got bonus. Over a "real" player, I'm pretty sure that forces are much more balanced ...
In game terms, I think the Soviet Union is pretty much perfect as is and just needs some minor tweaks like vet and certain unit balancing. Also, I do actually think that the higher up doctrine abilities should cost munitions. I'm sure the Ostheer will perhaps have 1-2 more men per squad than the Wehrmacht, putting an "Ostgren" (fictional at this point in time) squad at 5 men. 5 Ostgrenadiers to 7-8 strelky is pretty much the 2:3 ratio anyway. Soviets will also be slightly rebalanced to take into account the retreat function they will gain.
Though i could argue that russians did build huge fortified defense lines (f.e. Stalingrad, Kursk), captured germans (especially Waffen-SS) were also immediatly shot and germans too had their late war militias (Volkssturm), I wont, because it wont lead to an end.