Buffing sov stock T3 and T4 and giving heavy armor exploitable advantage will.
Ostheer already have proven that tiger spam meta is there only because of players mentality and another doctrines work just as well(yes, I'll say CAS here).
OKW and USF doesn't need to and don't rely on call-ins at all, its alternatives for what they already have, but nothing you'd want every single game.
That leaves soviets who have no stock infantry or armor capable of taking on axis units of equal tier in any cost effective manner on the long run therefore the cause and mandatory need of call-in meta.
True. People talk about "Fixing the call in meta" like it's some kinda demon from another dimension and needs to be eradicated. All the arguments about increasing CP or tying them Either T3 or 4 etc are pointless in my opinion. All these suggestions prove that the call in meta is needed, but they just make it harder for the player.
Why do people do this taboo (using call ins)? Because they perform better than stock units. They are cost efficient. A tiger is cheaper than a panther, and can counter both infantry and armor.
Soviets: T34 becomes obsolete, SU85 is easy to flank, ISU and IS2s are tempting.
Ostheer: Teching, that is all.
USF: not as much popular as the other dations, but E8s and veteran rifles are tempting. You only sacrifice forward retreat point and if you play well, you hardly need it.
OKW: I think OKW is the only faction that is very well designed regarding the call-ins (not talking about balance). You have both main line (Volks) and elite infantry (Obers), you have access to light AI (PzII/FLAKHT), Light AT (Puma), medium AT (JgPzIV), heavy AT (Panther-don't argue about panther being heavy or not guys, it has huge HP and armor). They even have IRHT (not very useful, but it's there). Their units also scale very well (not only because of 5 vet system, Raketenwerfer's vet3 is amazing). So (despite balance issues) you have unit variety. In certain cases, you can rely on your call-ins depending the situation.
So, as any faction, if you can rely on your core units, you will only need call-ins as support, or for new unorthodox tactics. Imagine if you had access to T34/85s instead of 76. OR if you could buy a panther with the price of a tiger (or even less). Call in meta is when teching and core units are adjusted.
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If the teching is fixed for Ostheer, they will become the best designed faction IMO. But right know, you can't and won't pay for T4 which has great units. Aside from panther which is a good unit, both Brummbar and Pzwerfer are perfectly fine IF you can afford them. Brummbar itself is a beast. Good damage soaker, good versus defenses, team weapons, and even stuns mediums. But guess what, it's too god damn expensive to tech.