They actually have the best AT gun in the game IF you spend the muni for HVAP.
But for AT vehicles, the US have the fewest options. Stuart is the next best thing (not counting medium tanks for anyone). Ost has stug,panther, OKW has puma,jp4,panther, Brits have AEC, Firefly, Comet, Sovs have su76, su85
That doesnt mean the Jackson shouldnt be tweaked, but I think the reasoning for it being better than Firefly and su85 is the surrounding vehicle roster
Shermans are pretty good no?
When Axis rear armor are now 90-117, bunch of Sherman variations are your AT vehicles.