The Trusted Setup does not protect against an error in the code. The Zcash promise is that no one knows who or how much after it’s mined. There is no ledger to audit because that is the Zcash promise. It has been called its Achille’s Heel. Seeing the total does not mean there is not a hack that has tricked the internal method of getting the total. The reason bitcoin is so bloated is so that every user can see the entire history of each piece of coin. Nick Szabo has written at length that the history of an object being used in transactions can be key to it’s value, like someone’s great grandfather’s necklace being traded around in a group of 3 tribes. Remembering who owned the object for how long and how many cows it bought at each transaction is crucial.
See 51:30 in this interview with Zooko.