ISU takes 3-4 hits to kill a Pz.IV
Ferdi two hits Su-85s
Its underperforming against armour, not against infantry. Point clear?
Why should the ISU be super powerful against both infantry and armor? The difference in power between the elephant's AI potential and the ISU's AI is much higher than the difference between their AT potential. You really shouldn't be trying to fight off tanks with the ISU just like you wouldn't fight infantry with the elephant. This doesn't mean that the units are too weak.