Reading your comments, it sounds like you are arguing it is impossible to backup files in Dropbox in any reasonable way, and therefore nobody should backup their cloud files. I know you haven’t technically said that, but that’s what it sounds like.

I assume you don’t think that, so I’m curious, what would you propose positively?

> I know you haven’t technically said that, but that’s what it sounds like.

Yes, I didn't technically said that.

> It sounds like you are arguing it is impossible to backup files in Dropbox in any reasonable way, and therefore nobody should backup their cloud files.

I don't argue neither, either.

What I said is with "on demand file download", traditional backup software faces a hard problem. However, there are better ways to do that, primary candidate being rclone.

You can register a new application ID for your rclone installation for your Google Drive and Dropbox accounts, and use rclone as a very efficient, rsync-like tool to backup your cloud storage. That's what I do.

I'm currently backing up my cloud storages to a local TrueNAS installation. rclone automatically hash-checks everything and downloads the changed ones. If you can mount Backblaze via FUSE or something similar, you can use rclone as an intelligent MITM agent to smartly pull from cloud and push to Backblaze.

Also, using RESTIC or Borg as a backup container is a good idea since they can deduplicate and/or only store the differences between the snapshots, saving tons of space in the process, plus encrypting things for good measure.