You can reduce likelihood of any known risk with a preventative measure, in this case the permissions and ownership structure. That is good.
Backup does not reduce likelihood of risk.
It does something more wide-reaching, it mitigates against the bad outcome of loss (from most causes).So it defends from many unknown risks as well as known ones, and unexpected failure of preventative measures. It sort of protects you from your own ignorance and complacency.