I think you are mixing applications/programs with services, e.g. BackBlaze I consider a service whereas Arq and Carbon Copy Cloner (CCC) are applications that send files to many selectable locations.
In any event, since you asked:
Here’s what I do:
: iMac has Time Machine running continuously to a Synology NAS server, and two a connected USB drives. Also running Synology Backup onto Synology NAS for selected key folders, including DEVONthink’s. Backblaze also running taking all it can to provide offsite copies. Also, like you have a scheduled (with cron) AppleScript to do an archive Zip of the DEVONthink files once a week (those zip files captured in the regular backups). I keep a monthly copy of these zip files for a few years. .
: MacBook. Same as above but no Backblaze or Zip file export. Syncs with the iMac (Bonjour, WebDAV, and one small database using CloudKit)
: iPhone and iPad. Syncs with iMac (Bonjour and WebDAV on Synology NAS). CloudKit ready to go when needed for out and about travel. Use standard IOS backup to Apple iCloud entire device, which includes DEVONthink ToGo’s files.
: Synology NAS backed up daily to an attached USB drive and BackBlaze B2 sync, and Chronosync on iMac pulls important files from NAS onto one of its connected USB drives.
I test restores from TimeMachine at least a couple times a month if only because I want to restore back to a previous version of a file I am working on. Synology Backup files I look at log to make sure they happen. Pay little attention to Backblaze.
I’ve looked at Carbon Copy Cloner and Arq, but consider both basically the same as ChronoSynch which I’ve been using for years. I prefer Chronosync. If I wasn’t running Chronosync, I’d use the program “rsync” which is available on all Macs.
I do not consider DEVONthink’s sync to any server as backup, but is available in case a restore to a particular device is required.
I test these backups with test restores once or twice a quarter. Reminds me how it all works in addition to checking.
TimeMachine is particularly handy to restore individual files to get a previous version. I recall using it once to recover an entire DEVONthink which I deleted on purpose but then a few weeks later changed my mind.
Is all of the above secure? I hope and think so.
Over the top? Probably. But don’t care.