I use the IS-2 quite regularly. Thing is, if the Ostheer player does not have the heaviest of At, meaning Tiger/Elefant available, he has a serious problem on his hands. IS-2 dominates both P4s and StuGs, and comes in a doc that shines against Paks. The Panther on the other hand cannot really hurt infantry and can be almost safely ignored by itself - unlike ie. the P4 which can accumulate serious damage towards soft targets.
Except it only kills Paks its in range of. And if its not in range of the Pak its pretty much dead meat. Because the Pak has more DPS than the elephant. So if a Pak is properly positioned its going to kill the crap out of an IS2. Way more effectivley than a Zis can do to a Tiger even at Vet.
Because at vet the Zis gets close to a NON vet Paks DPS but its still shooting a target with more HPs. All you need to do to knock out an IS2 is faust it then Pak it. It will never get in range of the Pak since it moves so slow with engine damage and every other penetration of the Pak seems to give it a Star of Vet. Also even though Paks TWP is bugged you can still use it on a disabled IS2 since it cant really dodge the shot like faster tanks can.
IS2 is very much underperforming at its role assuming that now its role is to be equal to the Tiger in all things. Since I see the Tiger two shotting 6 man squads with a faster ROF and the IS2 sometimes 1 shotting 4 man squads (but NOWHERE NEAR what it used to do) and the fact they both cost the same...the IS2 is the crappy version of the two for certain.
Edit:
Also go look at what a Tiger does to a Zis this patch. Same effect about the same amount of time...takes less total damage doing it.