I think the main issue is not the bazookas and the lack of availability for elite bazookas, but the ATG.
SOV and UKF have two high penetration units: Their ATG and the heavy TD. To counter mediums, these factions can rely on their ATGs which allows to make their heavy TDs more vulnerable in some regards (casemate, slow ROF and movement). Against Panthers and heavier units, both units work absolutely fine.
But USF does not have that. Additionally, the mediums of the Axis factions are quite different in armor. Bazookas and especially elite ones work okay against the OST P4, not so much though against OKW's P4. Similarly, they are unreliable against Panthers, a fact which is also true for their ATG. So in the end to reliably counter a Panther, USF relies on building a vehicle themselves, the Jackson. All other factions could get another PaK to defend against a Panther after loosing their heavy TD or simply already having invested into a Sherman. USF still can't, even if officers get elite bazookas. The combo of Cromwell/6-Pounder or T34/ZiS can work against Panthers and OKW P4, Sherman/57mm does not work that great.
And before anyone mentions it: Yes, you can dump munitions into your ATG to make it really good against heavies, but in the end this only get's you so far in a faction that lacks mines and can lose snares in the late game after infantry wipes.
Jackson is the only unit holding USF's late game together. Any serious nerf - as reasonable as it might be from a design point of view - would probably kill this faction.
So in conclusion:
Touching the Jackson is a difficult unit, because USF relies on it to shut down heavy tanks. The current performance level of USF's late game AT capabilities seems mostly fine in my eyes. But heavier nerfs to the Jackson (especially it's potential against heavy units) probably cannot be compensated by having a bit better bazookas that work semi-reliably against mediums on 1-2 squads, because these bazookas could not fill the gap in the anti-heavy department. I think USF's anti medium power could stem a nerfed Jackson, but the anti-heavy department could not.
Thank you. Finally somebody that gets it. The whole faction is designed around the Jackson and people confuse that for "Being OP". Furthremore, you can't compare squads with zooks with vehicles. No matter how elite, werfer, stuka, MGs, mines can easily deny any infantry advance. Then there is also the zook range. It's not a far reaching AT rifle.
Nerf Jackson reload? A single panther can dive it (+ lack of reliable mines on USF)
Nerf penetration? Heavies roll over.
Nerf HP? LoL
Nerf Armour? It's already the lowest it can be for a tank so no point.
Nerf range? Elefant goes BRRRR even more. Panther goes BRRRR. Stug goes BRRR.
And to top all of that. Rifles need vet1 for a slow firing, long reload snare.
Whatever you nerf on Jackson, you kill the teamgame potential of USF and remember that teamgames are still all about heavy tanks, stukas, werfers and elite non doctrinal axis infantry and even mainlane infantry with MG42s (like cheap ostruppen which excel in cover, which is pretty much everywhere usually in teamgames).
You can't really expect to go vs Panther with a nerfed Jackson that can't keep it at range. An expensive tank, but still the best tank hunter in the game. Can solo take on any Ally heavy tank due to high armour, hp and penetration.