Even on the theoretical level of "what we could do if we had infinite patches coming up" I don't think it is a good idea to specialize ATGs to anti-heavy units. They are the earliest AT unit a faction can field and they need to be generalists to allow for combacks in case one player gets locked out of fuel or looses his tank early. In the current rooster, especially OST relies on them to counter light vehicles, but also OKW T1 builds absolutely rely on them. Similarly, OST's LV's potency would skyrocket until the Allied LV shows up. There must be an MP based counter to basically everything that can be fielded to ensure that the match is not automatically won or lost if one player destroys the other players expensive tank destroyer.
I also don't see the real point of the SU100 apart from flavor. SOV already has the light and heavy TD combination. It's just the design of the SOV early mid game that screws over the SU76 and forces you to buy a T70. Yes, SU100 could take the heavy TD place and SU85 downgrade to the light TD, but in the end this would just be name changes to the existing system (unless I completely misunderstood your point).
This whole chain of ideas was sparked by getting two Shermans and/or the Jackson into a better spot, but here I'd argue that it is better to redesign the Shermans instead of changing the sholw faction setup.
Sorry, I really derailed the thread with my ideas. I don't mean for ATGs to be specialized in any form; I'm basically saying Axis ATGs should be generalist, while Allied ATGs can toggle between being very good against lights and mediums without muni cost, or toggle to maintain capability against heavy tanks but for muni costs and slower fire rate. As for the Soviets, it's not just a name change, more of a specialization. SU76 just doesn't work as a medium tank counter IMO. Poor penetration, doesn't have the speed necessary, and it's multirole purpose means it can't be too good at either. I might be wrong but I tend to think of it as a light tank counter that can also deal with team weapons.
As for the issue at hand, yes, USF should have a Sherman redesign. Make HVSS/Wolverine stock, nerf the Jackson's fire rate or speed.