I think thats a cool way to balance it given how USF stresses as a faction mobility and firepower, not durability.
IRL it was basically a more armoured tiger I. That would be helluva boring in game since we already have that with IS-2/tiger...
Well I don't think that would be boring, but I suppose that's the more subjective side of things. I just think they went a bit too far with the mobility thing - to the point of being unintuitive (it's about the same size as those other heavy tanks, after all).