Yes and no. By 1943, the Germans were on the run and out of the assault business. However, in a defensive role firing from ambush, the Stugs with their low profile and powerful gun gave a good accounting of themselves. Using imitation as the best form of flattery, the Stug concept can be considered successful in that the Soviets and Americans developed similar assault gun platforms. Below is the American WW-II developed T-28:
Problem with the assault gun was its lack of a turret.
They were meant to accompany infantry assaulting a fixed position, hence the name assault gun.
In a defensive ambush the lack of a turret meant that unless you opponent came within a very narrow field of fire, you’d have to fire up the engine, turn the vehicle and very likely ruin your ambush.
America only built 2 T-28 prototypes. Germans built over 10,000 STuGs but their tankers still much preferred the Panzer III it was based on, smaller gun or not.
The late model Panzer III N had a short barreled 75mm gun but had a shaped charge round that could handle most opponents.