I somehow understand the OP in terms of defence. The IS-2 feels like a weaker tiger to me in terms of damage but the armor is brutal. It feels like only 25% of all shots won't bounce.
IS2 armor is 375/205, better than Tiger's 300/180(by 25%/14%), in exchange Tiger gets 28% higher ROF(5 vs 6.4 avg reload). Quite a fair tradeoff given Axis AT weapon generally have higher penetration values than their counterparts.
Panther pen 260/240/220 or 69/64/59% chance of front pen
Pak 40 pen 210/200/190 or 56/53/51% chance of front pen
Shrek pen 180/170/160 or 48/45/43% chance of front pen
P4 pen 120/110/100 or 32/29/27% chance of front pen
You have to be shooting IS 2 from the front with a P4 all day to feel like only 25% of shots won't bounce.