Ever considered to raise Jackson pop by 1 instead?
Its much better than firefly with the same pop.
It also got crew repairs that doubles as jump out build more units trick.
Pftt no way. All TDs and heavy-med armor pops are way too high as it is. All TDs like Jackson, Firefly, Jagpanzer IV, should be no more than 14 pop and all later game T3/4 tanks like Panther, Churchill, Comet should be no more than 16 pop.
Beyond that there is literally no reason to change the Jackson other than to appears complainers. It is a TD with 0 anti-infantry ability and is rather mediocre against super heavy armor like the Jagtiger, King Tiger or the Ferdinand. It is good against medium armor and Panthers but why that an issue when it's supposed to be good against those things?