UPDATE! (yay)
I finally got around to playing with the stubby gun in the MA.
So, with compared to the M5/75HE:
Splash dmg is much reduced with the panzer. In the MA with the M4 one could hit a building and it would do enough dmg to the one across the street so that the next round, carefully aimed at that opposing building would destroy both. This is not the case with the panzer.
Notable, buildings when receiving two direct hits with the panzer seem somewhat reluctant to explode (they do, and this may be a function of lag, but I have only experienced it with this tank) They have somewhat of a delay as if it takes ALL of the dmg to register to destroy it.
The reload time is also significantly longer than the M4/75
End result, the gun seems great for EW, and seems great for scenarios, but is of little use in the MA.