Can you remotely delete all the data and backups? (It's an honest question; I'm not intimately familiar with AWS but from glancing at the documentation it seems that even glacier archives can be deleted without delay)
Because if you can, then so can an attacker who has sufficiently compromised your business.
edit: I see some stuff about "vault locking" which might do the trick. Are you using that to protect your data?
https://docs.aws.amazon.com/AmazonS3/latest/dev/Versioning.h...
And then keeping root user credentials on a cold storage laptop.
Vault lock seems to be for Glacier, but it'd still be worth looking into for cold storage backups. More layers of defense are always good.
"S3 Object Lock can be configured in one of two modes. When deployed in Governance mode, AWS accounts with specific IAM permissions are able to remove object locks from objects. If you require stronger immutability to comply with regulations, you can use Compliance Mode. In Compliance Mode, the protection cannot be removed by any user, including the root account."
https://aws.amazon.com/about-aws/whats-new/2018/11/s3-object...