Well on the ZSU-57-2 the two guns are a modified variation of the ASU-57 which do have high pen. And what would you prefer to do? Shoot down planes (Which can either spawn in the dozens or just not spawn at all) or fight tanks?
Plus if you want an AA capable with a less of a learning curve you can go for the WZ305 which gets he-vt.
In the end,the ZSU-57-2 is AA but has better AT use and that would go for every other AA