P47's are supposed to be used against heavies, they don't do very well against mediums specifically because it would be OP as hell due to the lower health of medium tanks.
Really the only thing about the P47 that bugs me is the fact the rockets do a fuckload of damage to infantry anywhere near the tank.
The Ostwind and Scout car should not be relied upon for AA, especially against P47 spam. You pretty much HAVE to make a Flaktrack later in the game if your facing an P47 spammer('s).
I once got a Flaktrack to vet 5 just by shooting down planes lol.
At strafe of OST is doing a lot of damage, for heavy tanks, mediums and infantry. It is very universal and good vs all units. So it is not fair, if expensive p47 only good vs heavies, it must be good vs all tanks.
At strafe is doing big damage for infantry too, so it is fair.
Also, I don't see problem in making flaktrak for countering planes.