True, but that’s also a common reason people don’t do backups at all. What I’m noting is that you could look at it not as a disadvantage but as enforcing best practices. 
The thing is, it seems to me like even tools like restic are components, rather than the whole story. The odd thing about Syncthing is how many people seem to think it’s the only piece they need. Maybe it’s because the commercial sync services tend to encourage people thinking they’re good for backups?