You're making the Jackson being hard counter to both categories at cost of not being good vs both of them at the same time.
Today the Jackson is not good vs mediums, it is just the best option because Sherman AT sucks. I mean Stug or jpz4 are good vs mediums at cost of being casemate but stug is cheap and jpz4 has insane stats for its price.
Your solution isn't really going to solve the issue. As Ostheer you not going to have at the same time Pz4 and Pz5 (unless big game mode) so jackson will still be hard countering everything you deploy by selecting one or the other mode. As OKW, Pz4 and Pz5 will be countered by the low accuracy/High pen mode and PUMA/Jpz4 by the other one.
Don't get me wrong, as USF fanboy I'd love your idea to be implemented. But as a player seeking balance, not really
Imo, its better the make sherman AT being superior to what it is today and Jackson being only low acc/high pen etc.. mode
Today the Jackson IS GREAT vs mediums because it still retains the mobility, accuracy, Shots to kill (200 dmg low RoF still required 4 shots to kill a medium tank) while having the extra 160 HP to survive and the improved RoF on vanilla shots.
The Jackson would be better if it was a Firefly clone basically.