I think there is a better solution. Give stug range 60. Don't change anything else. You could make it a bit more expensive.
Generally, range is the most important factor. Stug has no turret. Should be perfectly counterable. Most players don't realise that in tank battles the ability to make your opponent dive is the most lethal, if you have more range your opponent will have to dive to even have a chance of penetrating your armour. A diving vehicle does not have a line of sight - the defending vehicle will have it, and will shoot at the attacker while the diving vehicle may have problems even connecting shots. On top of that there will be other units supporting the kiting unit hitting the diver. This is when most damage is done and often the diving vehicle will get snared (sometimes with satchels).
Yes good points all around. Certain attributes are more determinstic than others for certain roles
But i still go for heat ap ammo as a vet bonus for the 3 wehr tanks.
It is a tested out come, easy to implement and a mixture of vipper selectable ammo idea.