1. All other factions have a lot of very mobile units, so USSR here is not uniqe.
2. Cheapness of units hardly compensated with their powers. Same T-34-76 is weakest middle MBT tank in game. If that would be same powerfull as Pz4 for that price - I would agree that cheapness in benefit. But here it is compensated and nerfed with lower efficiency, so what for I need cheap, but totally weak or useless units?
3. Flexibilty with conscripts? Such as? They are worst mainline infantry in game. Very slow rate of fire, low and random accuracy, worst grenades in game equiped with... USF Riflemans are flexible, since you can give them different guns, Tommyrifles are flexible with side upgrades and same guns... Conscripts? Just trash. I don't even use them, since I learned how maximspam works.
4. About Teching and Tiers. T1 is absolutely useless, since it has only 1 (!) real combat unit - snipers. Penals are infantry without purpouse today and M3 Car... Buying that is just throwing your money on nothing. And situation with T3/T4 is very strange, cos I mostly don't need T4, since SU-76 became so effective, that it can punch down even King Tigers, lol. Only reason to build T4 for people today is Katyusha. And T-34-85 sometimes.
5. About "Great doctrines". They are no more great, than all other faction's doctrines. That's ridiculous, that USSR getting with doctrines that kind of units, which other factions have in stock! All normal (not good, normal) infantry - in doctrines. All normal tanks - in doctrines. That doctrinal addiction of USSR is not their plus, but minus. It just cripples them.
1. America is the only one with nearly as much as mobility as Soviets. Soviets got sprinting infantry, fast set up machine guns and super fast light vehicles.
2. For the cost of one OKW PzIV you can nearly have two t-34's. Two beats one everytime.
3. Molotovs are cheap and effective, AT grenades are excellent. Merge lets them support other squads. Sandbag cover is solid and builds quite quickly. They're fast and cheap, making them great flanking and capping units. With doctrines like hit the dirt and PPSH they became a real threat as well.
4. Penals are great early game, they got way better damage than scripts up close and the flamer is a solid choice. Satchel charges are also pretty useful against bunkers and houses. M3 is also plenty useful when used properly.
5. Soviets doctrines are the highest impact on playstyle by far.