Soviet teching along with ostheer needs a general redone its not nearly as efficient and rewarding as the okw and usf teching. Another issue soviets have is the over reliance on call ins because of their inefficient teching and awful tier units. A fix would be ofcourse buffing the stock units
This is one of the most important changes that have to be made in the next balance patch. Soviet T3/T4 is way too expensive for 120 fuel and Wehrmacht teching is overall terrible.
Teching for both vCoH2 factions is pretty lackluster compared to the new WFA factions which is one of the reasons why the call-in meta exists. People tend to skip T3/T4 to wait for call-ins because teching is too expensive and because some units are simply not worth it.
Soviet fuel costs for T3/T4 should be reduced to something around 100 fuel and once you've built either T3 or T4 the other building gets cheaper. Then, some units should receive minor buffs like the SU-76 (penetration/health increase) or the T-34/76 (slightly less scatter for example).
Wehrmacht teching could be changed this way:
Costs for Battlephases: 100MP + 20 fuel
Costs for buildings: 100MP + 40 fuel (T2), 100MP + 60 fuel (T3) and 100MP + 80 fuel for T4.
This would also make the USF vs Ostheer matchup less problematic due to the reduced MP drain.
Once teching has been adjusted for Ostheer and Soviets, call-ins should be reworked by introducing a fuel penalty for having more than one heavy tank on the field and/or simply limiting the number of heavy tanks a player can have at the same time.
Teching for Soviets/Ostheer has to be brought in line with the new factions.