Agree except for the part about the mortar - the mortar isn't used because the only thing it's adequate at is dispensing smoke and barraging buildings, and 240mp is usually a little steep for that at that point in the game. The AOE profile is simply too jank to be useful for dealing damage, even with the barrage, which is itself no more accurate or reliable than the autofire.
I just checked the stats on the USF vs the WM mortar. The WM mortar is a bit better. I thought they were the same though. Maybe the stats are out of date.
Either way, if you heavily change the functionality of the pack howitzer then I agree that the mortar should be buffer slightly to compensate. You could just make it a clone of the WM mortar. Of all the units that can be mirrored of each other the regular mortars are the ones that make the most sense to do so. I’d still give them different vet 1 abilities, but I don’t see any other reason that mortars shouldn’t all have the same stats on auto fire and barrage. Soviets can still have six man crews though, it’s not that much of an advantage in most games and can make you bleed more manpower in mortar vs mortar fights anyways.