Captain won't...
As I say, I agree that the sherman would have been the better choice and that you may well have been able to close out the game with it.
I disagree that your teching choice cost you the game though, I think with the units you had at the point you hit captain you could have still closed the game had you played it differently.
Yes, captain bunches up when firing his bazooka making him a walking disaster vs the stug-e but there are plenty of buildings on stalingrad that could be used to keep the stug away, particularly when coupled with your AT gun.
Plus, you could have dodged major tier all together and just floated to 9cp and grabbed an easy8 as soon as it became available (to be honest I don't see the point of going lt-captain unless you plan to do this with either armour or rifle companies)
On the subject of the OP: I agree that TWP is a strange vet ability of the stug-e but I kinda think the stug-e is only OP because of the cover bunching nonsense and the fact that its a call-in tank in a call-in world.