Correct - you are wrong. 
But more accurately, I’m not clear. LOL
While the API has no access to the non-tabular elements, the Email Pack apparently has some internal magic that allows non-tabular content to be transmitted via email messages. This forum thread touches on a lot of these issues. If they would expose this magic to Pack developers, a far better backup capability might be possible. Until then, a hybrid approach could be contrived in something like Google Apps Script that watches a dedicated inbox for content and then uses the Coda API to gather all tabular content, thus blending it all into some sort of unified backup schema stored in Drive, Firestore, sheets, whatever…
Reversing this process - i.e., mitigating disaster recovery - is an entirely different story.