Neither ZiS nor SU76 have anything to do with the Brummbar. Such is mentioning the SU76 being an assault gun as a response to Esxile's claim. It simply has nothing to do with the discussion.
There are multiple ways to balance abilities, but tying them to cost alone creates heavy differences between modes.
Making abilities powerful and expensive will lead to strange cheese tactics, making them weak and cheap might make them feel useless and not worth the micro effort.
The damage the ZiS barrage does is in order for 35-ish munition in my opinion. I would not screw around with that too much since it feels in line with other abilities. If the issue is spamability, CD might be the way to go.
The same way you can spam grenades on late game when floating on munition or whatever other ability in fact.
One Zis can't spam its barrage everywhere in the map because its still a clunky unit to move that also need to be available to counter tanks. I maintain what I said the problem occurs when you got two of them as per meta and then: or you got a windows frame to use both of them on a single location for a devastating effect, or one of them while de second is kept a bit further to protect it from tanks flanking it.
IMO if you start nerfing the CD you'll basically make it way worst to use as single unit and enforce people to build two of them to overcome the CD nerf.
On a side note, isn't possible for the moderation to speak with Vipper about his semantic pedantic attitude. Honeslty should we always lose so much time and effort to bear with its semantic arguments on every topic like him making the SU-76 the equivalent of the Brumbar because they both have somewho the denomitation of assault gun IRL but are completely different in game.