Its not that its invulnerable. It is fast and well armed and can take a base. Why not perk it?
it's neither fast nor well armored, I agree nice gun with a good amount of ammo.
Top speed is 53 K/hr, 32-33 M/hr onroad and 10K/hr, 6 M/hr offroad(I seriously think the offroad speed is a mistake) . So, considerably slower than the M-3.
A maximum of 15 MM of armor would make it very vulnerable, even to 7.92 MM and .30 cals.
Open topped and no room for troops,what with the gun mount and amunition storage.
I still don't see why it would be perked.