Im just going to spoil the idea of what we have brainstormed for the jackson and FF.
-Jackson far pen down: you still get your 60 range jackson and can outrange panthers, but maybe it shouldnt be so reliable at that range...
-Jackson fuel cost up: the jackson is a premium tank destroyer (again, basically the best in the game), but its price doesnt really reflect that. Its the only dedicated AT vehicle usf have, and people argue its high performance is a necessity for usf. So then keep its performance, but at least make sure players have to pay for that performance.
FF cost down: same deal. FF performance is okay, and performs well against heavies relative to the other TDs, but its the most expensive allied TD by a sizeable margin, and thats just not very justifiable. I personally want tulip costs decreased (one of the other things that makes the FF distinct from other TDs besides its damage; sad that theyre too expensive to be practical) but thats not currently in the draft.
That approach will not solve the issue that allied TD are very effective vs ALL vehicles.
Imo one should be more creative. One should test creating 2 set of rounds similar to Sherman 76 and use them to balance Super heavy tank and medium tanks separately. Unit meant to Counter Super heavies could have access to "AP rounds" with range, accuracy, penetration and ROF design vs those units , while normal round with characteristics better suited vs mediums tanks.
One could ever take a bit further increasing the target size of Super heavies (maybe decreasing of other vehicles also) so that thing become easier to balance. Finally one can create more interesting profile for vehicles and create a "flanker" clash that would benefit the most from engaging enemy units close.