I think tigers are fine. You can deal with them just fine with AT guns and non-doctrinal tank hunters. You can also do well against them with flanking non doctrinal medium armor.
I think IS-2s need a nerf to their armor. They can absorb too much AT gun/JP4 fire from the front and they are a lot less vulnerable to flanking axis medium armor than the tiger is to allied medium armor. The Panther is the only non-doctrinal unit that can successfully deal with the IS-2, which gives the axis a lot less options and battlefield flexibility than the allies.
*This post is only about the performance of these 2 units. On a whole-army basis I think both tanks are OP as neither requires any investment in tech*
