Why are you not supporting/sighting for your Jacksons.
Also; Who cares if it has less DPS than the SU-85? The SU-85 rarely has a chance to make that matter, and the extremely high damage shot of a Jackson can easily keep PIV's and whatnot out of the fight.
Because the purpose of the Jackson is to counter even the heaviest armor thrown at it. Since its the top dog. If using Panzer 4s then the Sherman and ATG work fine. Even Zooks work OK if you can stand the MP bleed.
To site for the Jackson is to put other units at risk. Which either bleeds your MP from units getting Tigerd to death or puts armor at risk.
So being able to self sight is an advantage and not a small one.
So lowering its damage and increasing its Pen will make using P4s more rewarding and also allow the Jackson to work as the counter to heavy tanks that the USF requires.