Making teching a requirement for all call in's, not just Soviet ones would help extend the game out a little bit and make Axis heavies like the Tiger and Jadgtiger/Elefant require more investment just like the Soviet call in's would.
The assumption that call in meta is only a problem with Allies ignores the fact that if call in's were tied to tech then having to get T4 would delay the Tiger a lot.
Soviets wouldn't have an issues because they wouldn't have to fight enemy call in's either, fighting Ost stock units with Soviets stock units isn't that hard at all, and USF and OKW stock units are great making it easy for them to hold out.
