Remember than Aimed Shot does stuff other than stop tanks turrets from functioning. It would be a buff to the StuG III, not a nerf.
Being unable to act or do anything for 3-4 seconds is worse than having your turret locked because you will score a tank kill rather than letting it reverse out to fight another day.
Either TWP for the Stug should be like Aimed Shot(but no ability to fire on infantry, etc) or when it hits, it lowers the effectiveness of the vehicle. Maybe a 10-15% reduction in speed, 35-50% reduction in rate of fire and turret rotation so the vehicle can still fight, but is less combat effective during that duration.