This armor does not help, because almost all hits on the IS-2 are penetration. But at the same time he has a disgusting gun. That's why he has disgusting performance. Because this "armor" IS-2 does not buffed. Reduce the armor (it's almost always penetrated) and improve the performance of the gun. That's why I think Pershing is a very good tank: I don't expect armor protection, but great mobility and gun. IS-2: armor almost penetrated (it is rather a miracle that the armor is not penetrated), main gun is terrible, low mobility.
You do know that most stock allied TDs have more penetration than most axis TDs.
You do also realize that if is IS-2 does not have enough armor Panther is even in far worse spot.