Buff Panther main gun penetration so it's better against the IS-2 without becomming impossible to deal with in team games. Decrease IS-2 vet bonus range to 45 instead of 50.
There we go, easy fix. Now axis has a counter to the IS-2. No need to nerf a faction into oblivion because 1 doctrinal unit is too good.
I don't think its a good idea to buff Panther's penetration to counter ONE DOCTRINE unit, not to mention the implication it would have vs USF and Brits.
Also, not everyone picks IS-2 every game!