What about simply making GVs more resistant to bomb explosions so as to require greater accuracy to have effect with bombs?
That's a slippery road...
But I tell you GV guys what one of my personal 'adjustments' would be - reduced perk loss for GV's when being bombed by planes.
The problem is the perk cost largely reflect the capability of tanks in ground combat, as it should be. The Tiger II for example substantially outclasses its opposition and thus fully deserves the 100 perk price tag. Or the JagdPanther its 30 perks (actually I think they are still rather low)
But when it comes to planes&bombs, both are about as much sitting ducks as any other tank. And unlike perk planes, there is nothing much you can do about it, if someone else decides to bomb ya, he will bomb ya. You can't fight him, you can not run away, and you can hardly evade. You can only stay at home and sit on concrete, ready to .ef
And that's one reason why you see so few of them going out there and fight their equally powerful brethren - because one of them has to leave home for that and will soon have a bomb on its head.