Reload on the move, reload without risk of decrew, turreted, with higher speed, theoretically wiping stuff more frequently, and... Royal Blitzkrieg?
Wait, isn't it vet 5 Sturmtiger?
Its smaller AOE makes it more fair. Your example of 4 AT units shooting at the churchill makes sense but I've had the same thing happen with the strumgiter.
The range on the strumtiger mixed with its large AOE and ability to fire through LOS blockers make it a broken unit. Even in the alpha the AVRE had no were close to the range of the strumtiger.
Either reduce its range or make it so it cant fire through buildings and large AOE blockers and see where the unit goes. No one ever said to balance a game you need to do large super changes.