4 units holding together an entire faction, the fact that this is the top method of using the usf is damning evidence that the overall design is a bit off (they're not weak just one dimensional)
Indeed USF sacrifies units for multirole units.
Being balanced around a T0 mortar is too much to ask apparently 
It would slow USF down imo, thus progressing more into the late, which is fine as well for the USF imo.
Mortar is just not needed for the fact USF got a pak howie and an argueably bad scott.