> Authentication is handled separately from the database itself. A breach of a single database host, even as root, would not mean you're able to view the data in plain text or have access to the keys.

A breach of a single database host isn't even going to tell you who the data is associated with.

> It could be decrypted in stream. User authenticates into the system, it then grabs the encrypted data in the database, decrypts it outside of that host using their key and sends them the decrypted data.

Yes, it could be. It hardly matters. Unless it is E2E the key to decrypt it is there on the host that sends it. They just compromise that host instead.