There is nothing wrong with Sherman perk price, it is as soft as a panzer and if I spend 15 perks on a Sherman and some IL2 dweeb kills me I will be royally PO'd.
The Sherman is not as soft as the Panzer. Nope. If you really want to see this, it's not hard to test. Just take up a T34/76 and have at it. You will kill Panzers with frontal armor and turret hits in the T34/76 all the way out to 1200-1600 yards (not every shot, but the kills will happen on average with X number of such hits). You will neither turret the Sherman from the front, nor kill it with hits into the hull from the front, at any range you choose. From the side you will kill Shermans with the T34/76, but you won't do it from the front. And you will kill the Panzers from the side even more easily.
Also, the T34/76 will rarely kill a Sherman from the rear - it will usually kill the engine, but not destroy the tank. The T34/76 gun will, however, kill Panzers outright with shots through the engine block. Just ask anyone who has camped a VH before.
Bottom line is that the Sherman is a tougher nut to crack than the Panzer, and has a monstrously powerful gun. Both of those advantages, not just the gun alone, contribute to the Sherman perkworthiness.