First off, let me quote my first response to you which got drowned off.
With that out of the way, no, the tank that you're putting on a pedestal is not that much better than a Panzer IV which still has many advantages with far better veterancy and Panzer Tactician access, and MG, and Axis has heavier tanks than IS-2 in the form of King Tiger and Jagdtiger. Panther is also a very effective non-doctrinal AT.
Panzer IV never ceases to be useful; it can hold its own well against IS-2. Just not alone and not very cost effectively, but it's by far not to be considered useless. It's not less useful than T-34/85 either, which it itself is not bad.
And edit to respond to your edit: T-34/85 would be perfectly balanced at T3 and would not need to be nerfed. At all. It's a slightly better Panzer IV that's still worse in many ways.
PIV:
Hitpoints:
640.0
Armor:
180.0
Rear armor:
90.0
Max speed:
6.3
Cost: 125 fuel
Pen: 120.0/110.0/100.0
t34/85:
Hitpoints:
800.0
Armor:
160.0
Rear armor:
80.0
Max speed:
6.3
Cost: 140 fuel
I wouldn't call that big on an increase in pen and health to be "just a little bit". And again, at T3 you would be getting those 85's out around the time Ostheer is just getting t3 done, never mind t4.