Depends on the reason why you need a restore. If something botches many databases at once (because the filer holding them dies or whatever), you might be looking at a fun time restoring hundreds or thousands of databases with a playbook that was meant for one or maybe ten databases and thus isn't sufficiently automated.
Not saying that these kinds of errors are likely. But you cannot just make these assertions without the context of your actual threat model. Same for the "better separation" part. How much separation you need depends on what you're protecting against what.
Depending on that answer, you may be interested in using row-level security: https://www.postgresql.org/docs/current/ddl-rowsecurity.html