The unit needs a nerf, no denying that, but if its underpowered it simply won't be used anymore and there goes the heavy armour support for that doctrine - it will ruin games for axis players going up against IS2s.
Nerf away, but avoid the knee jerk reaction brought on by soviet bitterness. Be smart about it.
I'm just saying, from a balancing process standpoint, it's much better to shoot low then to keep a unit op and exploitable. If a unit is too weak then it just doesn't get used and doesn't effect as much. When a unit is op it becomes heavely used and effects the entire game. Remember guards motor was a heavely used doctrine even when the T34-85s were broken.