Who use mg on stug ? Maybe Dane only, its waste of ammo, for unit that attack from shadow .
If it did something it might be used. Ostheer normally have a difficult choice at this point - go P4 first to help against the enemy infantry but anticipate it will soon get wrecked by an enemy tank or go Stug to destroy expected incoming enemy tank but lack any AI support to the point that enemy infantry can walk up to the stug and look through its ports to say hi to crew. All armoured vehicles should frighten infantry a little bit (Unless they are a Ferdinand at Kursk).