The FIREFLY is an improved Sherman, yes. The Sherman is the Sherman and we don't have one. 
Curious because I dont know not because im trying to be sarcastic.
With the improved gun on the firefly. was the armor improved as well?
Shermans were known as "Purple heart boxes" or "Ronsons" because of their notoriously weak armor and because they caught fire so easy "Lights first time every time" Its main assets were their speed, ease of maintenance & repair & great numbers produced. (It was a gangbanger)
Yet armor on the Firefly here seems abnormally tough to me.
As for the tiger
In addition to its thick armor he Tiger was lethal at greater ranges then anything we have in game but particularly against the T34 Which if its modeled that was would justify its perk value.
Thing is, here with everyone liking to camp and get in close both its armor and superior killing range are negated.