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I would say that the only flaw of the is-2 is that its pretty much an obese t-34/85. You can stand your ground vs individual german tanks (up to panther level), but you immediately lose initiative if the panther you're fighting has any sort of support (or multiple unit combinations that match the cost of your is-2), and will retreat. If the enemy has stronger armor (JT, elefant, king tiger), you lose the game outright, these hard counter the is-2 and there's nothing you can really do about it.
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In sort the "flaw" is that one can counter the unit:
1)by Supported Panther
This is not really "flaw" a Panther role is exactly that to counter heavily armored vehicles. The real problem would be if a supported Panther couldn't not counter the IS-2 since axis would have no stock option and they would have to use the same doctrines again and again
2)by JT/Elefant
These more expensive dedicated TDs are doctrinal and their role is exactly to counter heavily armored vehicles. The real problem would be if these heavy TD couldn't not counter the IS-2 since there would be no reason to even purchase these units if they couldn't deal with an IS-2
3)by KT
A more expensive in cost a tech heavy tank.
So no, there is no flaw in IS-2.
About bringing nothing new to the table, that is not really IS-2 fault. People complain about KV-2 so it was redesigned to be closer to IS-2 and now there are complains that are to similar.
If a unit need to change that would be KV-2 which is an assault gun and not IS-2 which is a heavy tank.