After playing some games recently i have to agree that a couple of ZiS guns with T34 and conscript support can create an area denial until you get to something more offensive, like an SU85. This especially works well on Minsk pocket to camp your fuel. Still when you add an ostwind to the mix your position is under serious danger since ZiS still wont hit and/or penetrate half the time.
My point is that i would much rather prefer ZiS to be a hard armor counter than it having 2 abilities and six man crews. I still _have_ to support this multi-purpose hard-to-kill AT gun just as i would have compared to a german PaK gun. So if i still have to do this why should i sacrifice solid AT capability? I just see no point in that. Barrage ability _is_ useful, but soviets have a dozen similar options to pick from. And when facing armor you need solid AT much much more.
I think they work as a hard armour counter. They're not offensive tank chasers like the SU-85 (which is still fairly OP in my view) but they can get a pretty good creep going and they synergise really well with the rest of the Soviet army (so, barrage to clear houses and MGs, extra sight ability on vet is pretty helpful when you suspect shenanigans). I think it needs less support and is less of a liability than the PAK right now, and the six men also makes it generally better at its AT role.
Ostwinds are really the only thing that can ruin their day right now, which is kind of inevitable if you don't have specific target tables. Again, compared to how badly the PAK-40 deals with T-70s (badly), T-34s (mixed), KV-8s (terribly), SU-85s (alright but not great), the ZiS seems to be in an alright spot to me right now. Making them cheaper I think would be too spammable, making them higher damage seems a bit risky when the survivability's so good. The PAK needs something else, I think, atm the vet ability's the main thing going for it and it's pretty hard to actually get the vet because it's so likely to get decrewed.
Edit: just seen your last posts - in short, I think the ZiS is pretty good (i.e. reliable, more or less) at AT and very useful for support, while the PAK's AT is lackluster against most of the things you want it against and it has no support capacity. Would support the PAK being a bit cheaper (like, 300/320) and a bit higher damage to discourage the anti-infantry tanks from just trying to take it head on.