but is a traditional database cryptographically secure? if a super user with write permissions (or, say, direct access to the physical data store) modifies records are users able to validate the integrity of the data?
You could use permissions and stored procedures that ensure append only.
The difference is that client applications does not need to trust proper "append-only" permissions were enforced on server side but they will be have the chance to detect any tampering while in the former approach, it won't be noticeable
Users just need to insert signed data into the database for tamper-proofing.
that's basically what I do in bigquery sometimes just with a time or timestamp column 'last_updated' and a uuid