EDIT: in other words, my question is actually whether your claim has relevance, considering how most crypto currencies aim to be public (or that's at least my impression).
If it's just an application level shielding, as in a separation between user software that can't access the information but a layer/cluster of infrastructure software that can, then I'm not so sure if its nothing more than rather meaningless cosmetics.
Do you by any change have some references as to how this would work? because I sincerely believe that this statement of "decentralization means access to all" actually fundamentally holds.
EDIT: I'm also doubting the classification of decentralized, if a piece of the user software relies on something else that has more capabilities (essentially a typical trait of centralization).
In Zcash or Monero, everyone knows the public blockchain and their own private keys. If you make a transaction, it's broadcast to all nodes. There's no special privileged nodes that people give their keys or transaction plaintexts to. Transaction data doesn't contain the sender, receiver, or amount in a way that's clear to the public. The transaction is made so the receiver can decrypt enough to see that they're the receiver and see the amount. The transaction also contains exactly enough information so that the public can verify that the transaction didn't invent any money out of thin air and instead only sent as much as the sender could, whoever they were. (Zero-knowledge proofs can be made to prove pretty arbitrary results over data even to people missing certain inputs!)
Confidential transactions combined with bulletproofs [0] are an efficient way to deal with the added privacy.
You cannot see who sent you the amount. Blockchain is fully encrypted and you cannot see any amounts or transaction sender/receiver.
Any real person using DeFi or NFTs is not using a privacy coins