Forts do seem to be built too quickly. You can even build level 2 forts in 2 turns.7) I've worked out how to generate level 2 forts in about 4 turns, early on I was planning these months in advance, towards the end they were being put together just behind the current front.
The tank losses from the combat model are way too high. It probably didn't help that Loki was playing on the new test patch that probably has reduced axis AFV losses.As Roger mentioned above the last Tank battle was the final straw. I lost 6-8 weeks of tank production in a single week. It would take months to rebuild the 40% of my Armoured force that was affected which is frankly ridiculous.
Not going to lie, it seems like there was something off on your offensives from '42, and an inability to sustain offensives. This resulted in fewer guards units than you need and a catch-22 where you can't win battles efficiently because you don't have guards units and can't promote guards units because you can't win battles. The guards promotion process has to start in the first winter where the axis can't counter attack and you get ungodly amounts of manpower fed to the Red Army.Not being able to achieve breakthroughs/encirclements or being able to attrite the Axis leaves the Red Army with no feasible warfare options. Coupled with that the LW still roamed about flying 100's of sorties. When there's over 50+ Axis fighters engaging any VVS force it's normally game over loss ratio wise for the VVS.
My solution to the air problem is to overwhelm the Luftwaffe in one section of the front. In a certain area, there's usually only 3/4 fighter groups covering a single section. These same groups will fly over and over again, and they will eventually be ground down. These groups can easily lose upwards of 50% of their fighters in a turn. Once they've been reinforced by bad pilots, their performance drops significantly.
The Germans don't get nearly enough 'trained pilots' each turn to replace all of their losses, so they either get no replacements, or they use untrained pilots. Since they have a very limited amount of fighter groups, the Germans can't really afford to send them to the reserves to train. On the other hand, the Soviets can train thousands of untrained pilots each turn, and cycle hundreds of fighters per turn between the front and the reserves, providing a continuous base of quality fighter pilots. If they concentrate their fighters, you can just bomb the rest of the front, killing thousands each turn with IL-2's. The air war is definitely a self reinforcing loop-back, and casually fighting the Luftwaffe here and there will just ensure they have their fighter groups stocked with invincible 99 xp pilots.
Lastly, that SU composition is not ideal for holding pockets. Tank brigades should only be used on attack, since they melt on the defense - as shown in that last battle.
Apologies if I'm being too critical, but I think a lot of the issues you faced were game-play issues and not systemic game issues - not that those don't exist. Hopefully others can read this and avoid some of the pitfalls that I thought I saw.