The difference between su-76 and stug is similar to the difference between zis3 and pak40. In both cases the soviet unit can have the additional AI capability by using the barrage, but the german one is much, much better in its primary role - AT.
Think about it.
The german Pak is better at dealing damage, but thats not important, because of the range.
U cant engage on maps like Charkov or Poltawa, where u cant flank em without being seen 2 minutes before.
It just does not work because of the barrage. If he spots ur paks he barrages on em, and even if he loses one SU76, ur paks are lost too. and one SU76 is so cheap, it doesnt hurt at all, because u dont need to hurry up teching to SU85.
Same with stug but as AT.
It switches that fast between barraging and AT, u cant counter that anymore. beside the SU76 is either his mates inf or his own, ur wehrmacht mortar cant engage because of the sowjet mortar, which is superior, but only vs mortar.
If u attack with stugs, he runs instantly just in front or even between them, takes 1!!! loss by getting crushed and throws his AT nades, and byebye stug. Same works with panther, but at least u have the chance to get him home and repair.
Thats my experience since patch.
And im no complete noob, i know what to do with Wehrmacht. Yesterday, played vs Crossfire and VonAsten, lost it in 20 min, played after that vs some lvl 9 to 10 noobs with 180~ hours and COULD NOT see any difference.
Its a specific build order, and he can nearly do what he want, he cant lose that.