Syncthing is more of a synchronization tool and less of a backup tool. For e.g., if I screwed up a file on one machine, that will automatically be replicated to other machines. Dropbox, on the other hand, "can" be used as a backup tool because I can go and recover an older version if I want.
I do know that Syncthing has a way to keep older file versions around for awhile but I find that a bit cumbersome to use, especially during restore.
So, I am curious to understand more on how you use Syncthing as a replacement to Dropbox. (I'd love to do the same but don't for reasons I wrote above.)