You're already a high-ranked OST-only player; you should already have the answer to how powerful the Stug will scale to the late-game, despite the changes. Especially in-light of the mega-buffs to the Ostwind.
If you can't figure that answer out for yourself, play some allies for a change for inspiration; especially USF and Soviets.
Can you replace the stug TWP ability with heat shells that only increase pen and not damage? so that it can scale better into late games without making it OP vs weaker armored vehicles