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.
It will also 1v1 panthers @ frontal armour 30% of the time, while it outperforms in AI against everything axis has.
Having worse vet is debatable. It's a flanking tank, rather than a long range slugger. It punishes turret-less tanks if you can come in wide.
Of course it's stats are different. Different in a way that makes it more useful. It's faster w/ good turret rotation, better AT DPS, better AI DPS and in a pinch it can cap a point.
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.
The argument of being doctrinal is a cost is a bit of a stretch. If that were true, than all doctrinal units should be AS cost efficient as the T35/85 and then everyone would be using doctrinal units rather than core units, which was a huge problem in the game a year or 2 ago.
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.
There are a lot of things that need attention. When I play soviets, I almost always choose a doctrine w/ the 34/85. It's also worth noting that the most widely used soviet Doctrine in the last ESL tournament has a t34/85 in it. I believe it had a large margin of the second most used doctrine.