> - backups are not encrypted by default so plaintext of your private chats can be obtained

Yes, but importantly not by Meta themselves.

> - Meta data of your messages is not encrypted so meta can make a graph of who you talk to and when

Fair enough and worth mentioning. I'm personally fine with it.

> - even if you enable encryption for backups all it takes is for the other person in your private convo (or a person in a group chat) to not enable it for your messages to be available in plaintext

Yes, but how would you prevent that even in principle? I can't control what the people I'm messaging do with their copy of my messages. As long as there isn't unnecessary non-repudiation (e.g. by the sender cryptographically signing all outbound messages, which the Signal protocol intentionally avoids), I think this is fair as well.

I do agree that e.g. vanishing chats with a short timeout/"view only once" images should probably not be included in backups, though; last time I checked, I think they were.

> Yes, but importantly not by Meta themselves.

Don’t they save backups to Meta? Even if not, they can read whatever’s (unencrypted) on your phone if they really want to.