Don't you understand why it cost 80 fuel? It is actuall T3 unit (like Pz4), which is putted in T4. That small price is not compensation of lack of power, but compensation of such late come. Just calculate, how much fuel you have to spend for to call first T-34-76 in combat and when it happens, compared with same Ostheers and Pz4.
If you build all the tiers....
Sov:
15 + 20 + 85 + 90 + 80 = 290 fuel for the first T-34/76
Ost:
15 + 40 + 20 + 45 + 75 + 125 = 320 fuel for PzIV
OKW:
15 + 25 + 15 +60 + 15 +120 + 15+ 150 = 415 Fuel for PzIV
Get rekt son.