I don't know why you treat it as a revelation that the best AT brawler in the game combined with the best ATG in the game can actually deal with a hybrid unit at one of its weak spots. I would rather say this is quite expected.
My point is, contrary to what some people seem to claim here, it does not take whole might of ze Fatherland to tackle ISU, all it takes is a player who knows it and knows how and when to engage.
Now more to the point: provide some data on your claims, because my calculations say otherwise.
In your scenario - 20 range, ISU vs Panther - the ISU has the same offensive performance as a SU85 with an expected TTK of 32,8 (ISU) vs 32,9 (SU85) (with very slight estimations regarding pen chances since I don't have the tools with me to make a 100% accurate calculation).
I suppose clarification is in order, so the whole situation was flanking it first in a place it couldn't retreat from easily(rammed itself on that northen trenches on crossing) and at least 1 shot at panther was HE. Yes, there were 2 ZiS guns protecting it, but they were frag bombed into atoms instantly.
Hopefully that clears things a bit.
Bumrushing anything is always bad idea, but 80% of people discussing balance here seem to be playing the game by setting rally point on opponents HQ and then building random units, going by situations they themselves are describing.
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