the t34/85 is better than a p4. it doesnt need another cost reduction. also, t34/85 spam without teching was far too common last patch for a reason. there was no incentive to tech when call ins came out so early.
P4 have 3 MGs and can shoot planes.
34/85 have lower scatter.
P4 have more armor and will deflect shots more often.
34/85 have hp to withstand 1 more shot.
P4 have much better vet ability and can acquire awesome doctrinal ability.
34/85 is doctrinal, P4 is not.
Thats pretty equal to me and again, considering 34/85 comes 4-5 mins later due to CP change, I don't really see a reason why it would cost more.
Even 1v1 against P4 can go both ways, depending on RNG purely, unless 34/85 attacks rear.
It wasn't not that much for call-ins being spammable, especially in 34/85 case as it was that soviets could finally use general use med tank that wasn't obliterated by german armor.
People will still skip T3 and go for 34/85 simply because it works.
To have 34/76 same appeal you either need to crush opponent, cutting his fuel for the most time or use soviet industry so you can overcome weakness with quantity.