You have a ability that is called "piercing shot" or something like that, ever used it? also playercard grittle?
Still, Jaeger armor would counterpick what was meta at that point (ISU or Artillery). If you were not worried about arty, you could also go for Fortified armor and have smoke to counter button + IL2 bombing strike cheese.
EVEN with mark vehicle, you would had same dmg as Ele with lower RoF AND like 60% chance of pen. Piercing shot was not guaranteed to hit in the same way TWP work at that point IIRC (hit ground not tracking unit). And tell me how could you surprise an ELE with an ISU when you had 150 sight range with focus sight + spotting scope or recon planes ?
ISU was not meant to destroy other tanks or be able to present a fight to the Ele, it was there to kill your AT guns + infantry so you could then push it with your own Zis + Guards + mediums (or just to be honest, the blob of double T3485s).