This is true in a sense “most modern SaaS apps have at least two unrelated users or user groups” (forgive me please if I’m wrong here, but that’s how I loosely understand “multi-tenant”), but it’s not exactly clear why this is important.
I strongly suspect that the majority of modern SaaSes don’t do any database-level tenant isolation or per-tenant backups. The smaller the company the less it’s likely. Row-level security is a very rare sight to behold, even in regulated areas (certifications like HIPAA compliance don’t really require this). The best they do if they’re really global (I’m sure most are only global in “we accept users from anywhere”, but not so much under the hood - even though cloudy sales pitches love to paint a different picture, most SaaSes I’ve seen were one or two-region deployments) is try to move/shard data closer to the the user’s region.
I think one concrete example (as simple as possible) would help a lot.