Why do you call it medium? It's closer to heavies not to mediums. Anyway I'd prefer Panther to IS2 - the closest Soviet non-doctrinal analogue is T34-76 (ha-ha), shittiest medium tank in the game. Lone Panther will be destroyed by combine mines/at-nades and IS-2 for sure if Axis player is stupid enough not to use blitz and smoke. But it never acts on its own. Blobs and packs usually support it. So destroying this piece of junk becomes even more harder. I think, Panther definitely needs nerf - armor and/or speed.
And your glorious IS-2 is not supported by an ATG and maybe a maxim/shock squad? Or maybe use incendiary barrage on their PaKwall? IS-2 is not an iWin button, neither is Panther.
This looks like a rage post. There are guys here trying to help you, listen to them instead of repeating you argument. Provide a replay and ask strategists for help dude.