OST faction get to have only a single stock casemate TD, because panthers are more like a heavy tank with good AT rather a heavy TD.
If panthers were Heavy TDs as jacksons are, they could reliably destroy another heavies like KVs, Churchs, IS2, ISU, Comets.
*Spoiler alert: Panthers cant cost effectively win against those heavies, as we all know, they trade hits as much and can loose miserably when the allied player has 3 functional neurons, axis can only spam panthers to get an advantage. So it cant be considered a heavy TD. At most an hybrid of heavy+medium TD
USF also have ATG, handheld zooks and some doctrinal variations to compensate AT power, like OST does with Elephant and OKW with JT.
And before people get their pitchforks and start a riot, soviet conscript dont have stock weapon upgrades and thats ok, now usf has great doctrinal AT units but they never appear in the discussion of jackOPns. GG then...
And which are these "Great Doctrinal AT Units" that USF has?
I took a look at my Commanders and found none of them, unless you mean Elite with Zooks or the P47s, or you mean the M10? (lul)
Either way the Jackson (And to a degree the Scott) are the reasons USF now can lategame, you nerf either of them and the faction will start to limp again.
Now having no early dominance nor lategame units.
Edit: USF has no Tank Hunter, Brick or such units to endure damage, so they get mobile high TDs instead. Fits the flavour and design of the faction.