They come in pairs but you pay for each of them so in theory you should have equal number of PzIV on the field and you should have your tanks earlier unless outplayed by your opponent.
You can always go for Panthers whenever you see Guard Motor being used just to be absolutely sure however a pair of PzIV or a PzIV supported by a PaK or StugIII should do the trick.
If you loose to a pair of T-34/85 while having a pair of PzIV then that's not a balance issue.
that's half true, you will never see 2 85's vs 2 pzIV cause germans have to pay for teching which is about the cost of a tank,given u skip t2 which add other costs,instead russians can just skip all techs and go straight for 2 medium armor without building cd on 7 cp,really embarassing,the only thing keeping at bay this spam is the tiger which casually is another call-in-notech-bomb.