That is 100% on you then, ost has multiple methods of forward healing and reinforcement stock.
Even if you keep reinforcing, ISU will keep dealing consistent bleed form 70 range. That is the OPness.
Its the exact same case with brummbar and brummbar is much more oppressive because
-it arrives earlier
-it costs much less
-it shoots twice as fast
-it always hits, contrary to ISU which has highest scatter values in game
To use Brumbar you have to be attack ground master (just like using puma your micro has to be perfect). Byt most important point (explained by Hannibal) is that Brumbar has to be in range of all AT guns/AT tanks to even shoot. It will be almost in a snare range (hoorah cons, button guards are very likely to snare it). The risk on it is so much greater than on ISU.
We've just had a tournament where 1 of these units was used predominantly and performed above expectations consistently. That unit was not ISU. If ISU was half as potent as you try to claim it, it would be used more often.
My personal belief is that ostheer just lacks any more anty infanty units and ostheer player just use what they have.
ISU wasn't used much because such expensive heavies are rarely used in 1v1.
Flank it.
Do not go in frontally against all of the support that will stand IN FRONT of ISU and don't suicide a single panther, where is your own infantry support to clear ATGs?
If Helping Hans can deal with ISU using only Pumas, you certainly can do the same using panthers.
The problem with ZiSs is that they will clear your support units more often than be cleared by support weapons based army themselves. Additional problem is the abundance of snares on Soviet units and the best in game mines. Generally rushing ISU is very risky.
While using stuka on vehicle is indeed unlikely scenario, ele itself hardcounters ISU badly, mark target or not, Ele will destroy ISU before losing 30% of own health consistently.
And no, ISU can NOT do both jobs from 70 range, its AT, as already established yet you chosing to ignore it all the time is OK at the very best and in context of all AT units in game, its plain bad, moreover, since you already forgot it, ISU needs to switch ammo, it means it can do AI OR AT, it can NEVER do both, because it doesn't work that way.
It is You who keep ignoring any competition results, not me. You also keep ignoring certain changes that have happened to the game in recent years.
Not doing both things at the same time means very little (God forbids it could shoot at tanks and infantry simulaneously!). As an ISU owner you CAN choose what you want to fight depending on your opponent's composition and in game situation. It is a great advantage, especially with so much range.