Actually I think it's better than the IS2, it just lacks in the AT department and is specifically an AI vehichle. If we wanted an AG/AI we would build a Brummbar which is much better at that job.
Panzer IV isn't as cost effective as it was. As ost you are facing Cheap TD spam, better 85mm anti-everything donks, etc.
I think reducing the fuel cost to 100-110 would help alot. Just make those vet2 skirts a purchasable upgrade so that would make it more balanced(IE no free HP increase.
Elite RM/DshK to Easy8/M4c are only effective if you aren't dealing with poopchain43 blobs or PAK walls and you also had a massive early game advantage.