- if it's a Proof of Authority is like a way to deal with who has access to write to the db

- the distributed consensus part is well researched (Raft, Paxos etc)

The only advantage that I can think of is interoperability: you will be able to communicate with the public blockchain for point in time "backups". Also, building your internal smart contracts you can use an existing language like Solidity.

This is indeed much more inefficient compared to a centralized solution and it's very difficult to create a decentralized network that can handle the amount of transactions that VISA processes for example.