Maybe because that Sherman would have died before "many many" hits were scored on you? Did you see my numbers on the previous page of this thread? The Sherman, while having a fantastic gun, and really good armor, isn't as survivable as the Tiger is. Sure, if someone ups a Tiger you can up a Sherman and have a great chance of killing him, but if the enemy are in Panzers and T34s, the Tiger is like King Kong.
Anyhow, yeah, I think the Sherman is perked too low. I'd like to see it be more like 1/2 or even 2/3 of the perk cost of the Tiger, not 1/3 or 1/4 like it is now.