Minus teching cost.
Panther needs some buffs, but it is indeed very tricky unit to balance. Maybe indirect nerfs for call-ins, small blitz buff (in current form blitz is just useless) and little fuel cost reduction will help?
Do not forget its AI capabilities. t-34 are simply excellent at destroying AI . Dedicated counters should be far more cost effective then the generalist tanks as you are taking a huge risk with it.