Saying it's to good for it's cost is the same way as asking for a cost increase, which would at least be better than making it only affect your own units.
Again; as others have pointed out in order to be consistent this would require FHQ to not affect allies, the CPIV to not affect allies, the ambulance to not affect allies, ect.
The factions have units in them that work well when paired with the other faction, this is by design and is not unintentional. The C-Panther is a large investment at 200 fuel which means that you won't be facing a Jadgtiger, regular Panther, or a King Tiger for a long time, it's appropriately CP timed and costs 25 more fuel than the regular Panther already.
And OKW call units are either A. Utility infantry or B. extreme late game tanks; the only faction in the game that can avoid teching to it's last tier is Soviets thanks to the way the faction is designed around call ins.
Try playing OKW with only T0 units and see how far you get. You need Mechanized HQ to deal with Soviets/USF early game, and you need Obers and P2/Sturmtiger to deal with blobs mid game. The Panther is necessary to bridge the gap to late game.
Right because the only way to balance an over performing unit is a cost increase.