It's too cheap because by every comparable standard it out performs axis armour for the cost.
If your argument is "because it's a doctrine unit," why are there a number of other doctrine units that are practically useless for their cost?
OH has crazy cost effective scout cars that mess up 70 fuel light vehicles in pairs. Just as that needs a fix so does the t34/85. Probably in the realm of 20 fuel.
The thing is it doesn't outperform by every comparable standard. It wins 1v1 against other meds and is superior in the AT role. It also has worse abilities, worse vet, worse stats in some other areas.
Being doctrinal is in effect a cost, because by choosing a doctrine with t34/85 you have the opportunity cost of the other doctrinal options you forego. This is especially true for sovs which are still quite reliant on doctrinal units. On the other hand you forego nothing by building core units. Of course that doesn't excuse doctrinal units being OP but you can't just dismiss it out of hand. True that many doctrinal units are useless but that doesn't mean the t34/85 must be, it just means those useless units need a buff or a rework.
Sovs are in a pretty good place right now. As always there are some things that need attention but the t34/85 doesn't need to be high on the priority list. If it truly does need a nerf then 5 fu would be acceptable, 20fu is just absurd and would see it relegated to uselessness.