I know, but our DBMS doesn't support schemas. Instead, it's easy to spin up more "databases" that all share one instance but have separate ACLs, quota, backups,

I know, but our DBMS doesn't support schemas. Instead, it's easy to spin up more "databases" that all share one instance but have separate ACLs, quota, backups, etc. Postgres has something similar but with less isolation. It doesn't really matter how exactly you slice it, point is you aren't sharing tables.