It is not so difficult to make the USSR more resilliant to the german attack. All you need is a little tweaking of the obvious....
- 1. Weather effects are cruelly ignored almost in this game, you can advance at high speed and fight even in blizzards, and those are rare. Frozen ground gives a higher malus bonus then snow! Hardly any MP is lost when your army camps in teh winter of 1941 to await the easy spring of 1942 and finish the job. Increase speed reductions in bad weather, give a heavy penalty for fighting and an even higher + for defending to the russians only.
-2. Ground unit output. Pathetically slow, you do historical pockets but USSR cannot recover as it takes ages to build one infantry divisions, let alone a tank division, they try, but they don't even have the time, so it's a classic case of YOU don't suffer enough and they suffer TOO MUCH, as the AI doesn't create pockets on you! So you don't HAVE to rebuild, just re-supply with MP. USSR created massive armies in months, true, badly supplied, but then make the russian infantry worse to the german one, give nation specific infantry. Only thing you can do is dramatically decrease build time and cost from the time you go to war with USSR for ALL units. Dramatical means half build time and half cost cuts, believe me, I tried and it takes them even then months to get a decent army. This is because only 50% is at the front, the rest moves around (no dig in bonus) and wonders the great eastern plains or sits around in Finland. I do not even consider this an AI cheat but a bare necessity!
-3. Soviet economy and help from the west, none existent! (almost) Thousands of planes, guns, trucks, tanks etc were delivered, which equipped the USSR army in 1941/42 until their economy got back, in this game, the USSR gets some supplies...
-4. Battles, important battles a human would fight to the death, the AI gives up, so battles need to be scripted, nobody likes this but then hey, make a better AI... Battle of Moscow/Leningrad/Stalingrad. Militia, forts, and AA created by event in cities, it works and is great fun! I have Leningrad impossible to take but surrounded and they get supplies by event, sometimes I manage to break, but mostly not, and if I do, at expense of other fronts, just like it should be.
I have a whole range of events for this and it has taken much testing to match it to a human, but it does now. But nobody wants them... I like 'm and keep hoping for improved mods in the meantime...