If you have the system backup(s) and the data in a partition of the system HDD, effectively you are only securing yourself from user error. If the drive goes bad or if you get ransomware/virus you still have no solution.
Unless the drive with the backup is offline or in the cloud / network don't consider that you have a backup.
I too have an SSD to boot and an HDD to store data in. For emergencies I've got a bootable USB with windows setup always available.
I should backup to one of my old drives, but I can't seem to find the time/energy.
For my work computer everything is in the cloud, so I don't really care.