How long are you keeping backups in cold storage for - usually you'd want maybe 6 months there, but no more, otherwise it's just going to grow unbounded and become a financial burden.
That's certainly a valid point, but it still doesn't solve the problem of having to remember to delete something in the event of data loss.
As far as I can tell to comply with a deletion request with absolute certainty requires infallible storage (which would remove the need for backups) or modifying backups (which contradicts the concept of a backup). Maybe you can claim 'force majeure' at some point, but perfect compliance seems impossible.
