I mean it is not mobile, but the PaK's stun is pretty good.
I'd say Ost has overall decent stopping power available with their PaKs and Fausts, not sure why the StuG blind (/or do you want a real stun?) needs to be available earlier.
On the other hand I also don't think that the change would cause a lot of issues, since the StuG is not a preferred TD anyway.
Here's the thing, At late game with all the chaos your paks can get decrewed(pretty easily) so does you mobile stun option. In it's not like you can buy your way out of that.
I see both blind and stun as in the same boat.
To be fair it's not specificly the stug I wan't to buff it's just that I wan't something that can give that option an is always available either weak and risky to use or decent but expensive.