It's only a problem if you don't know how to deal with it.
Edit:
I fought against ISU-152 yesterday. It was 2v2 and we lost it but only because my ally didn't exactly know what he was doing. Surely ISU-152 delivered a punch but at any time I didn't feel like I am unable to deal with that threat, to kill it off. Quite the opposite. If only my team mate had listen and flank with me we would have won it.
ISU-152 and Elephant are only OP on Rzew summer and Pripyat but since both these maps were removed from ranked rotation it doesn't matter any more. As far as rest of the maps go you have plenty routes to flank it and take it out even without any damage.
