IS-2 were design to hunt Tigers and I think Relic is trying to mimic this in the game. This could be the reason for recent Tiger nerf.
IS-2s were designed as breakthrough tanks. Their large gun was meant to bust bunkers and emplacements. With that rate of fire it couldn´t fight tanks that well. The trajectory wasn´t flat either. It was very hard to aim at long distances. If we go by design: The Panther was designed to counter tanks, the IS-2 wasn´t.
Complaining that you can't deal with them with Panthers is like complaining that you can't deal with a PzV (Panther) using T-34/76.
That´s a huge exaggeration. T-34/76 couldn´t go through the Panthers frontal armor. The Panther however could go through the IS-2s frontal armor. Panther is an anti tank-vehicle. So is the SU-85. Su-85 can give Tigers a serious beating, so Panther should give the IS-2 a serious beating.
Sounds like you are proposing that the Soviet heavy tank shouldn´t be countered by non doctrinal stuff (Panther), yet the German heavy tank should be countered by Soviet non-doctrinal stuff (Su-85).
Why would I build a Panther? It sucks versus infantry. It can basically only counter T-34s and somewhat SU-85s. Yet a Panzer IV can do the job better for cost. What remains is that the Panther can somewhat fight versus IS-2s. Take that away and German T4 is a joke.