I understand your idea of making the jackson the last hope in terms of AT for the USF. But the fact is that USF always has a lot of AT in their infantry, plus a well balanced AT gun, plus almost always floating on resources (specially in team games).
That's relics and modders idea.
All factions must have cost effective TD that needs to fight even the heaviest of opponents armor.
And that well balanced ATG is still weakest ATG in game by a long shot in terms of penetration and is not reliable against heavies at all.
Resource float is hardly an argument, everyone floats in 4s.
Jackson doesnt need to be that powerfull to snipe KT or JT, because you invalide all of the others axis tanks aswell, specially OST: Panther, Tiger, P4, Stugs.
Hence Jackson penetration went up, but damage and therefore DPS went down, its stronger vs Tiger and KT, but it needs more shots and therefore time to kill Panther as well as leaves meds on more then 40 hp after 3 hits.
So as long as there are 300+ armor units on either side and allies do not have Panther like tank, "standard" TDs need to do the job, but they pay for ability to engage heavies with their DPS.
Remember how vet3 SU-85 was a murder machine against everything mechanized? Now its MUCH weaker against meds, but MUCH better against heavies. Same happened to Jackson and Firefly was always like that bar its first iteration of tulips.