Most lawyers seem to be advising the opposite, though, and say that backups are ok - do you have some knowledge here, or are you arguing the spirit of the law?
Backups are fine because they are short-lived. You obviously have a reasonable amount of time to implement a request for deletion, say a week or two.
If you are keeping year-old “backups”, that’s actually an archive. The difference shouldn’t be too difficult to understand because year-old data is obviously useless if you have restore your database.