Except it wouldn't. Because the panther exists it would be like trying to have the su76 preform all the Soviet AT duty and saying use mark target.
The JP4 is a great unit, it's just nor designed for heavy armour. Okw have 3 AT vehicles, gotta try and avoid overlap. Jp4 can return fire on allied TDs which makes it unique, make it also reliable against heavy armour and we have successfully recreated the allied TD problem except there ARE alternatives being cut off instead of being omnipotent due to lack of options.
I've always hated the "use a panther arguement". The panther has the penetration yes, but it doesn't have the RoF to take down 1400HP worth of churchill or even the IS2 without support showing up from your opponet. The panther and jp4 are both great vs mediums, but neither are stellar vs heavies. If we have the diversity to make both, why not specialize them. Taking down IS2s frontally is even a challenge for a panther given RNG is semi reasonable. The jp4 also wouldn't struggle as much if its veterancy was fixed and the IS2 armor was lowered.