Now, if Relic decided to add the USSR and give the ZSU-37 (which was produced by 4 pieces before the end of the war) and not, for example, the GAZ-AAA with a 25-mm cannon, then this would be a claim. And it is clear why they would do so - an easy way to balance.
As for the Ostwind, it is most likely just a popular tank like the Tiger, I personally would like to see the Flakpanzer 38 (t) in the game. And if we take the number of produced flakpanzers, then they were all produced in a limited number.