Waiting until you have enough cp's for call ins? not going to work obers and the luchs are going to tear you a new one. you still managed to get them? well their impact is significantly lower because of volk shreks(and the only reason why so many people want to nerf shreks).
I personally think it's quite the opposite actually. I believe volk schreck blobs are one of the major contributing factors to call-in meta. You wait till the call-ins because non-doctrinal soviet tanks can't stand against volks blob. Call-in tanks are more durable and have better anti-infantry capabilities, no point in trying to keep them at bay with T34s when one volley forces it to retreat and repair. For infantry, all you can do is to get shocks, spam snipers or spam maxims because Soviet combined arms turns obsolete very quickly against OKW.